9 Harvard computer science classes you can take online for free — including an intro course that's already enrolled 2 million people

In this introductory course, students will learn "how to think algorithmically and solve programming problems efficiently" using concepts like abstraction, algorithms, data structures, encapsulation, resource management, security, software engineering, and web development. They will become familiar with programming languages such as C, Python, SQL, and JavaScript, plus CSS and HTML.

Students will develop and present a final programming project to their peers. Altogether, the program should take 12 weeks.

Students will learn about data, design, scalability, security, and user experience. Using hands-on projects, they'll become well versed in writing and using APIs, creating interactive UIs, and leveraging cloud services like GitHub and Heroku. The class will touch on HTML, SQL, JavaScript, Front Ends, Flask, and more.

The class should take 12 weeks.

Learn about the development of 2D and 3D interactive games. Using lectures and hands-on projects, students will explore the design of popular games such as Super Mario Bros., Pokémon, Angry Birds, and more.

The class takes 12 weeks to complete.

In this introductory course to AI, students will learn to use machine learning in Python. Through hands-on projects, students will be exposed to the theory behind graph search algorithms, classification, optimization, reinforcement learning, and other topics. Students will also learn about adversarial search, logical inference, Markov models, and natural language processing.

It should take seven weeks to complete.

This is a variant of Harvard's introductory computer science course that's been designed specifically for lawyers and law students to impart a deeper understanding of the legal implications of a client's technological decisions. The original CS50 takes a bottom-up approach, but this course does the opposite. Instead, it begins with high-level concepts and related design decisions.

The class should take students 10 weeks to complete.

This introductory course is CS50 for business professionals such as managers, product managers, founders, and decision-makers so they can make technological decisions even if they're not specifically tech experts. Unlike CS50's bottom-up approach, this course is also top-down, emphasizing a mastery of high-level concepts and related decisions. Topics include computational thinking, web development, and more.

The course should take students six weeks to complete.

This is Harvard's CS50 course for students who wouldn't call themselves fans of computers. It's best for people who work with technology every day but don't necessarily understand "how it all works underneath the hood" or how to troubleshoot. Harvard designed this version of their class to help fill in the gaps. Basic concepts like hardware, the Internet, multimedia, security, programming, and web development are all covered.

The course should be completed in six weeks.

Here, students pick up where CS50 leaves off. They'll learn about mobile app development with React Native. Students will be introduced to modern JavaScript (including ES6 and ES7) as well as to JSX, a JavaScript extension. After hands-on projects, students will implement an app entirely of their own design in a final project.

The course will last 13 weeks.

Designed for high school students, this AP version of the CS50 course introduces computer science and programming and teaches students how to think algorithmically and solve problems efficiently. It also satisfies the College Board's AP CS Principles curriculum framework. Students can earn an AP credit for it if their school approves the credit and administers the College Board's end-of-year exam.

Students who earn a satisfactory score on nine problem sets and a final project are also eligible to receive a verified certificate from HarvardX.

This course will take students 36 weeks to complete.