cs50 - freeCodeCamp.org

Harvard CS50 2026 – Free Computer Science University Course

Beau Carnes — Thu, 05 Feb 2026 17:10:59 +0000

Harvard University's CS50 is one of the most popular beginner computer science courses in the world.

We just released the entire 25-hour CS50 course on the freeCodeCamp.org YouTube channel. This is the most recent version updated for 2026, with an all-new section about the impact of artificial intelligence on computer science.

David J. Malan is widely considered to be one of the best computer science instructors. He teaches this course.

This course provides an introduction to the intellectual enterprises of computer science and the art of programming. This course teaches students how to think algorithmically and solve problems efficiently.

Topics include abstraction, algorithms, data structures, encapsulation, resource management, security, software engineering, and web programming. Languages include C, Python, and SQL plus HTML, CSS, and JavaScript.

Among the overarching goals of this course are to inspire students to explore unfamiliar waters, without fear of failure, create an intensive, shared experience, accessible to all students, and build community among students.

Here are the lectures included in this course:

Lecture 0 - Scratch
Lecture 1 - C
Lecture 2 - Arrays
Lecture 3 - Algorithms
Lecture 4 - Memory
Lecture 5 - Data Structures
Lecture 6 - Python
Lecture 7 - SQL
Artificial Intelligence
Lecture 8 - HTML, CSS, JavaScript
Lecture 9 - Flask
Lecture 10 - Emoji
Cybersecurity

Watch the full course on the freeCodeCamp.org YouTube channel (25-hour watch).

Review of CS50 – Harvard's Introduction to Computer Science Course

Phoebe Voong-Fadel — Mon, 09 Jan 2023 22:20:27 +0000

Are you considering taking the CS50 Introduction to Computer Science course, but wondering if it's the right fit for you?

As someone who doesn’t have a computer science degree and was looking to learn the fundamentals of the field, I was in the same boat. That's why I decided to enrol on the course and document my experience in this article.

I'll provide an overview and review of CS50 to help you decide if it's the right course for you.

What is CS50?

CS50 is a ten week online and on-campus course which serves as an introduction to computer science. It's taught at Harvard and Yale University.

The course leader is Professor David J. Malan. He’s supported by the CS50 team, which consists of Senior Preceptors and an entire production team. The course runs from 1 January to 31 December.

Why choose CS50?

There are several reasons why CS50 might be a good choice for you. Here are a few:

It's a highly respected course offered by Harvard University. This means that you'll be learning from experienced instructors and getting access to a top-quality course.
It covers a wide range of topics, including computer science fundamentals, algorithms, data structures, and programming languages such as C, Python, and SQL. This means that you'll have a well-rounded introduction to the field.
It's self-paced, which means that you can work through the course at your own pace and fit it into your schedule. You can watch the lectures on various platforms, including EdX and freeCodeCamp's YouTube channel. For me this was important as I didn’t have a lot of spare time.
It's free! You’ll have access to the lectures and course materials.

What is the Format of the Course?

There are ten weeks worth of lectures, labs, and problem sets, which must be completed. At the end of the course, there’s a final project.

Is this a course for beginners?

Yes. In fact, around two thirds of students who enroll in CS50 have never taken a computer science course before. So if you're new to the field and looking to learn the basics, you'll be in good company.

That being said, don't expect the course to be easy. While the lectures are designed to be accessible and engaging, the problem sets and labs can be challenging. On average, students should expect to spend around 12 hours per week on the course.

Do I get a certificate at the end of the course?

You can choose to receive a free CS50 certificate or pay for a verified certificate from edX.

What if you don’t finish the course by 31 December?

You can roll over any submissions into the following year. I did this and the process was straightforward. The course content is pretty much the same with some updates to the course materials.

CS50 Walkthrough, Week by Week

Week 0: Learn Scratch

In the first week of the course, you'll be introduced to the world of computer science and learn about how numbers, text, and images are represented in binary.

You'll also learn about algorithms and pseudo code, and get a hands-on introduction to Scratch, a graphical programming language.

For your first problem set, you'll create a Scratch project. This week is a fun way to ease you into the course and get a taste of programming.

If you’re interested, this is my Scratch project, which was inspired by my son who’s fascinated by space.

Week 1: Learn C

In the second week of the course, you'll dive into C, a low-level programming language.

You'll learn programming fundamentals such as functions, conditionals, boolean expressions, loops, and variables.

For the problem set, you'll create a program that outputs a pyramid of hashes like at the end of a level in a Super Mario game.

Week 2: Introduction to Arrays

You'll continue learning about programming in C and delve into topics such as how your program compiles, debugging, arrays, characters, strings, and command-line arguments.

For the lab, you'll write a Caesar's cipher program, and for the problem set, you'll work on a scrabble-type challenge. If you’ve completed the JavaScript Algorithm and Data Structures certificate on freeCodeCamp, this should be familiar as this is one of the coding challenges.

Week 3: Introduction to Algorithms

In week three, you'll learn about different types of search (linear and binary) and different types of sort (selection and bubble), as well as recursion.

You'll also learn about big O notation, which can be challenging but is an important concept in computer science. Thankfully, the course provides additional short videos on more difficult concepts, which provide a more detailed explanation with examples.

Week 4: Computer Memory

Week four focuses on memory, including topics such as pointers, addresses, memory allocation and freeing memory, detecting memory leaks, and explaining how a stack overflow occurs.

The lab and problem set involve manipulating audio and image files. Below is an example of a filter I created in C.

Week 5: Data Structures

In the final week of programming in C, you'll learn about how pointers can be used to store the addresses in memory for linked lists.

The lab consolidates your knowledge of pointers, and the problem set involves creating a spell checking program. This was a particularly tricky exercise and it’s worth taking your time to understand the starter files provided before delving in.

Week 6: Learn Python Basics

Week six marks the transition from C to Python, a popular programming language that is easier to learn and use than C. You'll work on problem sets that involve translating previous programs written in C to Python.

Week 7: SQL and Relational Databases

In week seven, you'll learn about relational databases and SQL (Structured Query Language), using SQLite to execute queries on the command line and in Python.

The problem set is a fun one, as you’ll have to solve a mystery of who stole the CS50 duck through a series of SQL queries!

Week 8: HTML, CSS, and JavaScript

Week eight covers the basics of the internet and the web, including HTML, CSS, and JavaScript on the client side.

For the problem set you’ll create a home page about yourself.

Week 9: Flask

In week nine, you'll learn about Flask, a Python framework that is used to build web applications. You'll cover topics such as forms, layouts and templating using Jinja, POST and GET requests, and how to email from a Flask application. You'll also walk through the process of building a full-stack application.

For the problem set, you'll put your skills to the test by implementing a full-stack finance application that brings together everything you've learned throughout the course. This is a challenging but rewarding project that will give you a taste of what it's like to build a real-world web application.

Week 10: Wrap up lecture

No exercises this week. There’s a guest lecturer and a wrap up from Prof Malan.

The final project

The last part of the course is the final project. The brief is to:

“build something of interest to you, that you solve an actual problem, that you impact your community, or that you change the world.”

This is deliberately vague, so you have the freedom to choose any programming language and project you like. You'll also have to record a three minute video demoing your app.

I built a baby tracking app. On the backend I developed a REST API with Python and Flask. For my database I used SQLite. On the client side, I used React.js.

This is a substantial piece of work. From conception, to designing my application through to developing the app, I probably spent over 30 hours on this.

Your final project would make a great addition to your personal portfolio so have fun with it! Below are some screenshots of my application.

What Are the Benefits of Taking CS50?

The lectures are high quality, in terms of content and production. Professor Malan is animated, enthusiastic, and is very passionate about teaching computer science and programming. The visual examples on the stage and on the interactive screens are helpful for understanding difficult concepts.
The problem sets are well-structured and provide detailed walkthrough videos, specifications, and starter code with comments to help guide you through the tasks. You can also test your code to see if it meets all the requirements before submitting.
Setting up your integrated development environment (IDE) is straightforward, thanks to a modified version of GitHub Codespaces, which allows you to code in the browser.
The CS50 library is a helpful resource with great documentation. The library provides functions such as get_string, which prompts a user for a string in the command line interface (CLI). These functions act like training wheels during the early weeks of the course, helping you to focus on familiarising yourself with the programming language.
For some of the problem sets, there are two options: one for when you're "feeling less comfortable" and one for when you're "feeling more comfortable." This allows you to choose the level of difficulty that is right for you.
The course is structured in a way that builds on your knowledge from previous lectures and problem sets. You'll start with C, a low-level language, and then move on to how to implement the same things in Python and JavaScript later in the course.
There is a large and active online CS50 community on various platforms such as Facebook, Twitter, Discord, and LinkedIn, where you can connect with other students and get help with problem sets and labs.
The course is free and accessible to anyone with a computer and an internet connection.

What are the drawbacks of CS50?

The course is challenging. It can have a steep learning curve. I found I had to do additional reading around subjects I was not familiar/comfortable with.

Most people don't finish the course, but even if you don't complete it, you can still benefit from what you learn. In the words of Prof Malan:

“What ultimately matters in this course is not so much where you end up relative to your classmates but where you end up relative to yourself when you begin.”

Summary

CS50 is a comprehensive and highly respected course that provides a strong foundation in computer science.

As a self-taught frontend developer with no computer science degree, I found that the course was an excellent way to fill in knowledge gaps and strengthen my understanding of the fundamentals of the field.

The lectures are engaging and well-produced, and the problem sets are challenging but provide a valuable opportunity to apply what you've learned.

The course covers a wide range of topics, making it an excellent introduction to computer science. Overall, it is a standout course and one of the best online learning experiences I've had.

I hope you’ve found this article useful and it’s helped you with making the decision on whether to take CS50.

Harvard CS50 Guide: How to Pick the Right Course for You (with Free Certificate)

Manoel — Fri, 12 Jun 2020 17:50:20 +0000

In January, I wrote an article on Class Central about CS50, Harvard’s Introduction to Computer Science, which offers a free certificate. In this article, I'll go over CS50’s entire 10-course lineup, seven of which also offer a free certificate.

CS50: The Original Course

CS50 is taught by Harvard Professor David J. Malan. Back in 2015, when Class Central contributor Charlie Soliman reviewed the course, he said this about Professor Malan:

At the risk of stating a cliché, his approach to teaching is unlike anything I have seen and can easily be labeled as revolutionary. One can detect the joy and effort he puts into each of his lectures.

Having taken the course myself, I can say that this quote is as relevant today as it was back then. In fact, since the course is updated every year, it’s gotten even better.

CS50 in Harvard’s Sanders Theater

Offered at Harvard since 2007 and on edX since 2012, CS50 has grown to become Harvard’s largest on-campus course, with 800+ students per term. It's also one of the world’s highest rated and most popular MOOCs ever, with 2M+ learners in total.

And “CS50” has evolved from a code designating a single course to a brand encompassing multiple courses exploring different subjects, targeting different audiences, and stacking into different learning paths.

To make sense of CS50’s offerings, I partly audited each course, I explored their online communities, and I contacted their course staff. I found that Professor Malan often replies to emails himself — a nice touch considering the course has over 100 staff.

CS50: The Expanded Offering

CS50’s full offering currently comprises ten courses that can be broken down into three levels as shown in the table below. As you can see, seven courses offer a free certificate.

Click on a course or level to jump to the corresponding section.

Level	Courses	Workload	Certificate
Basic (Optional)	CS50 Tech	4 hours / 6 weeks	Free on Harvard OCW $90 on edX
Core (Pick one: usually enough)	CS50	12 hours / 12 weeks	Free on Harvard OCW $90 on edX
CS50 AP	5 hours / 32 weeks	No free certificate $90 on edX
CS50 Law	4 hours / 10 weeks	Free on Harvard OCW $99 on edX
CS50 Business	4 hours / 6 weeks	Free on Harvard OCW $90 on edX
Follow-up (Pick one or several)	CS50 AI	20 hours / 7 weeks	Free on Harvard OCW $199 on edX
CS50 Web	8 hours / 12 weeks	Free on Harvard OCW $149 on edX
CS50 Games	8 hours / 12 weeks	Free on Harvard OCW $149 on edX
CS50 Mobile	8 hours / 13 weeks	No certificates
CS50 Beyond	5 hours / 12 weeks	No certificates

Basic Course

Currently, CS50 only offers one basic course. It can be seen as an optional on-ramp to CS50’s core courses. If you don’t feel ready for a formal introduction to computer science, this is a good place to start.

CS50 Understanding Technology — CS50T

CS50T is a gentle introduction to the world of computing. It starts at the hardware level and works its way up from there. It explores how the internet works, how websites are created, how security is ensured, and ends with coding basics.

The course is taught by David J. Malan. It involves about 4 hours of study per week over 6 weeks. This course offers the following certificate options:

Free certificate via Harvard OpenCourseWare
Paid verified certificate via edX
Paid transcript and academic credit via Harvard Extension School

Core Courses

Currently, CS50 offers four core courses. These include the original CS50 as well as variants geared toward different types of learners. This is where most learners want to start.

One course should be plenty. But learners that take a variant may want to also take the original CS50 — especially if they plan to continue with a follow-up course.

CS50 Introduction to Computer Science

CS50 is Harvard’s computer science introduction. It starts with binary and goes up the ladder of abstraction from machine code to low-level languages to high-level languages. It explores algorithms, data structures, and memory management. And it ends with one of three specialization tracks: web, game, or mobile development.

The course is taught by David J. Malan. It involves about 12 hours of study per week over 12 weeks. And it offers the following certificate options:

Free certificate via Harvard OpenCourseWare
Paid verified certificate via edX
Paid transcript and academic credit via Harvard Extension School

CS50 AP Computer Science Principles — CS50AP

CS50AP is a CS50 variant that allows students in participating schools to earn AP credit. In the US, AP credit can help university applicants bolster their chances of admission and validate credit.

The course covers the same content as CS50 but includes more material, two extra assignments, and a proctored exam.

The course is taught by David J. Malan. It involves about 5 hours of study per week over 32 weeks. And it only offers a paid verified certificate via edX.

CS50 Computer Science for Lawyers — CS50L

CS50L is a CS50 variant geared toward lawyers and law students. Part of the curriculum explores similar content but emphasizes big-picture understanding of low-level details. The other part explores entirely new content that considers how law and computer science interact — for instance, in regards to cybersecurity, data privacy, and internet regulation.

The course is taught by David J. Malan and Doug Lloyd. It involves about 4 hours of study per week over 10 weeks and offers the following certificate options:

Free certificate via Harvard OpenCourseWare
Paid verified certificate via edX
Paid certificate via Harvard Law School Executive Education

CS50 Computer Science for Business Professionals — CS50B

CS50B is a CS50 variant geared toward business professionals. Most of the course explores similar content but emphasizes big-picture understanding of low-level details. A small part explores entirely new content relevant to businesses, for instance, cloud computing.

The course is taught by David J. Malan. It involves about 4 hours of study per week over 6 weeks and offers the following certificate options:

Free certificate via Harvard OpenCourseWare
Paid verified certificate via edX
Paid certificate and academic credit via Harvard Extension School

Follow-up Courses

Currently, CS50 offers five follow-up courses. These pick up where CS50 leaves off and explore a specific subject. They’re an excellent way to build on your computer science fundamentals by delving into a specialization.

CS50 Introduction to Artificial Intelligence with Python — CS50AI

CS50AI leverages the Python programming language to explore modern artificial intelligence. It covers foundational AI concepts, such as search algorithms and knowledge models, and builds on them to discuss more advanced concepts, such as optimization and machine learning.

The course is taught by Brian Yu. It involves about 20 hours of study per week over 7 weeks and offers the following certificate options:

Free certificate via Harvard OpenCourseWare
Paid verified certificate via edX
Paid transcript and academic credit via Harvard Extension School

The courses is also part of edX’s Professional Certificate in Computer Science for Artificial Intelligence.

CS50 Web Programming with Python and JavaScript — CS50W

CS50W explores the languages, tools, and processes underpinning modern web app development. It covers languages such as Python and JavaScript, frameworks such as Flask and Django, and services such as GitHub and Heroku.

The course is taught by Brian Yu. It involves about 8 hours of study per week over 12 weeks. This course offers the following certificate options:

Free certificate via Harvard OpenCourseWare
Paid verified certificate via edX
Paid transcript and academic credit via Harvard Extension School

The courses is also part of edX’s Professional Certificate in Computer Science for Web Programming.

CS50 Introduction to Game Development — CS50G

CS50G explores the languages, tools, and processes underpinning modern game development. It leverages languages such as C# and frameworks such as Unity to create 2D and 3D experiences, and draws examples from video games such as Pong, Mario, and Portal.

The course is taught by Colton Ogden. It involves about 8 hours of study per week over 12 weeks and offers the following certificate options:

Free certificate via Harvard OpenCourseWare
Paid verified certificate via edX
Paid transcript and academic credit via Harvard Extension School

The courses is also part of edX’s Professional Certificate in Computer Science for Game Development.

CS50 Mobile App Development with React Native — CS50M

CS50M explores how to develop mobile apps using the React Native framework. It covers concepts such as state and components, processes such as testing and deployment, and tools such as Redux and JSX.

The course is taught by Jordan Hayashi. It involves about 8 hours of study per week over 13 weeks. This course is offered via Harvard OpenCourseWare, but has no certificate.

The courses is also part of edX’s Professional Certificate in Computer Science and Mobile Apps.

CS50 Beyond

CS50 Beyond is the precursor of CS50W. It explores the same subject, web development, but does it in a more condensed time frame. Most topics remain the same, but many of the projects are different.

The course is taught by Brian Yu. It involves about 5 hours of study per week over 12 weeks. This course is offered via Harvard OpenCourseWare, but has no certificate.

Learn game design principles from Valve Portal developers

Beau Carnes — Wed, 13 Feb 2019 15:06:47 +0000

In this talk, Valve programers who created the game Portal discuss problems they faced in development and how they solved them. Leaning about how they solved Portal problems can give you insight into how to design better games.

This lecture is the final lecture of CS50's Introduction to Game Development course from Harvard University. The course explores principles of 2D and 3D graphics, animation, sound, and collision detection using frameworks like Unity and LÖVE 2D, as well as languages like Lua and C#.

You can watch the lecture on the freeCodeCamp.org YouTube channel.

Develop a Portal game clone with Unity

Beau Carnes — Tue, 12 Feb 2019 16:30:20 +0000

Learn game development principles by coding a Portal-like game using Unity and C#. The principles you learn in this lecture from Colton Ogden can apply to any programming language and any game.

This lecture is part of CS50's Introduction to Game Development course from Harvard University. The course explores principles of 2D and 3D graphics, animation, sound, and collision detection using frameworks like Unity and LÖVE 2D, as well as languages like Lua and C#.