You are enrolled
Every student in this course is enrolled in CS50x 2026 on edX. That gives you the same lectures, notes, problem sets and tools as Harvard’s students, for free, and an optional certificate if you finish CS50’s own problem sets.
- Course home: cs50.harvard.edu/x/2026
- edX: cs50.edx.org (sign in with the account you used to enroll)
- YouTube playlist: This is CS50 (the same lectures, public)
Before every Monday
Each week page has a Before class box that names the CS50 lecture we build on. The routine:
- Watch the lecture (about 2 hours; 1.5× speed is fine, pausing to type the examples is better).
- Read the notes. They are the lecture in text, with every program.
- Skim the slides so you recognize the diagrams when they come back on Monday.
- Optional: try the CS50 problem set of that week. Our labs are different programs on the same ideas, so the practice transfers directly.
Our Monday lecture assumes you did this. It does not repeat the lecture; it goes deeper, connects it to industry, and answers your questions.
Which tool for what
| Tool | Use it for | Not for |
|---|---|---|
| cs50.dev | Following the lecture, CS50 problem sets, quick experiments (make, check50, debug50 are preinstalled) | Our graded labs (those live in your Classroom 50 repository and open in Codespaces) |
| Codespaces | Our labs and your project | — |
| cs50.ai (the duck) | Explaining an error message, a concept, a line of code | Writing your lab for you (it will refuse, and so will the course policy) |
| Colab | The exploration notebooks on lab pages, including the C ones | Graded files |
Mapping: our weeks and CS50’s
| Our week | CS50x 2026 | Our week | CS50x 2026 |
|---|---|---|---|
| 2 | Week 0 · Scratch | 9 | Week 6 · Python |
| 3 | Week 1 · C | 10 | Artificial Intelligence |
| 4 | Week 2 · Arrays | 11 | Week 7 · SQL |
| 5 | Week 3 · Algorithms | 12 | Week 8 · HTML, CSS, JavaScript |
| 6 | Week 4 · Memory | 13 | CS50 Cybersecurity, lectures 0–1 |
| 7 | Week 5 · Data Structures | 14 | Week 9 · Flask (optional) |
| 8 | Midterm | 15 | Week 10 · The End |
Weeks 1 (introduction), 13 (hardware and security) and 14 (HCI and industry practice) add material that CS50x does not cover in the same way; their week pages carry their own reading.
Certificate
If you complete all of CS50’s problem sets and its final project on edX, you receive a free CS50 certificate from Harvard, independent of this course’s grade. It is a real line on a CV. Our labs cover most of the same skills, so the marginal effort is modest.