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CS50x: Introduction to Computer Science

Harvard's famous intro to computer science, from Scratch and C to Python, SQL and the web.

Taught byHarvard Online
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About this course

CS50x teaches you to think algorithmically, starting in C so you see what a computer is doing, then moving to Python, SQL, HTML, CSS, JavaScript and Flask. The 2026 edition also includes a lecture on artificial intelligence. Problem sets are demanding and the course ends with a final project.

Best for: Anyone wanting a serious, free foundation in computer science.

What you will be able to do

  • Reason about algorithms, memory and data structures
  • Write and debug programs in C and Python
  • Query databases with SQL
  • Build a simple web app with Flask

Syllabus and your progress

Tick modules off as you finish them on Harvard Online.

0 of 8 modules done

Plan your pace

At 4 hours a week you would finish in about 30 weeks, using the course time estimate above.

Progress is saved in this browser only. No account needed.

Cost and certificate

Free certificate

Free CS50 certificate from Harvard's OpenCourseWare for completing the work; an edX verified certificate costs extra.

Harvard Online sets the terms and can change them. Check the course page before you commit serious time, and tell us if something changed.

Quick answers

Is CS50x: Introduction to Computer Science really free?
Yes, the course material is free on Harvard Online. Free CS50 certificate from Harvard's OpenCourseWare for completing the work; an edX verified certificate costs extra.
How long does CS50x: Introduction to Computer Science take?
Plan for about 120 hrs in total (Editorial estimate; the provider does not publish a total. Eleven lecture weeks plus problem sets and a final project.). It is self-paced, so you can go faster or slower.
Do I need experience before CS50x: Introduction to Computer Science?
No. It is a beginner course with no prerequisites listed.

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CS50x: Introduction to Computer Science

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