See cs50.ly/puzzle-day-2... for a summary of last year’s CS50x Puzzle Day as well as some past puzzles for practice. Indeed, the best way to practice for this year is to solve past puzzles first!
The event is open to everyone around the world, whether taking CS50 or not. No prior CS experience required. Teams of size 2, 3, or 4 are encouraged, or you can participate on your own. Teachers are welcome to host their own version during class.
CS50x Puzzle Day is an online adaptation of an event we hold at Harvard each year, an opportunity to collaborate on a team with classmates, family, friends, students, and colleagues on a packet of puzzles (i.e., logic problems).
Hello, world! CS50x Puzzle Day starts anytime after 00:00 on Friday, April 3, and ends anytime before 23:59 on Monday, April 6, in your own time zone. Register at cs50.ly/register.
Missed the launch of the new-and-improved CS50x 2026? 🧐 Not to worry! Enroll anytime at cs50.edx.org or watch the entire course on YouTube at cs50.ly/x2026. All your progress from last year will roll over!
On January 1, 2026, we’re launching the new-and-improved version of CS50x on edx.org and CS50’s YouTube. A little sneak peek below!
Happy holidays from Professor @davidjmalan.bsky.social and CS50’s whole team here in Cambridge. 🎁 Stay tuned for release of CS50x 2026 on January 1, 2026.
youtube.com/shorts/8XuW8...
Tune in to CS50’s YouTube channel to watch interviews from the CS50 Fair. You’ll see students at Harvard present their final projects. And you'll perhaps be inspired for a project of your own! 💫
This is CS50x 2026 with Professor David J. Malan, CS50's (free) introduction to the intellectual enterprises of computer science and the art of programming, now with artificial intelligence (AI). 🦆 Full season available on edX on January 1, 2026. Register at cs50.edx.org.
Live from Harvard University at 1:30pm EST with Professor David J. Malan, this is CS50's last lecture this year. Open to anyone online. This lecture will become part of CS50x 2026 on edX on January 1, 2026.
On YouTube at youtube.com/live/NcBMUE1....
On Zoom at cs50.zoom.us/meeting/regi....
![Harvard CS50 prof David J. Malan on why you should learn programming slowly [Podcast #197]](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:3yifsv33q54vzl7mmzndmjym/bafkreighes436kf5j2cnmjtzfdahc2imr76rjthrzzaapytnrpfo3huzzy@jpeg)
Check out this podcast with Professor @davidjmalan.bsky.social and @freecodecamp.bsky.social teacher and founder @quincy.bsky.social, where they talk about how CS50 got its start, the impact of AI on programming, and the future of education.
youtu.be/ZK6XWSCCgPQ?...
Live from Harvard University at 1:30pm EST, this is Week 9 of CS50 on Flask. Open to anyone online. This lecture will become part of CS50x 2026 on edX on January 1, 2026.
On YouTube at www.youtube.com/live/F8w1K3C....
On Zoom at cs50.zoom.us/meeting/regi....
Live from Harvard University at 1:30pm EST, this is Week 8 of CS50 on HTML, CSS, JavaScript. Open to anyone online. This lecture will become part of CS50x 2026 on edX on January 1, 2026.
On YouTube at youtube.com/live/gPCuN4W....
On Zoom at cs50.zoom.us/meeting/regi....
Live from Harvard University at 12pm EDT, this is CS50's lecture on AI. Open to anyone online. This lecture will become part of CS50x 2026 on edX on January 1, 2026.
On YouTube at youtube.com/live/yD1Y1ch....
On Zoom at cs50.zoom.us/meeting/regi....
Live from Harvard University at 1:30pm EDT, this is Week 7 of CS50 on SQL and more. Open to anyone online. This lecture will become part of CS50x 2026 on edX on January 1, 2026.
On YouTube at youtube.com/live/kaA8eKB....
On Zoom at cs50.zoom.us/meeting/regi....
Live from Harvard University at 1:30pm EDT, this is Week 6 of CS50 on #Python. Open to anyone online. To attend in person some day, see cs50.ly/attend.
On Zoom at cs50.zoom.us/meeting/regi....
On YouTube at youtube.com/live/KV2Nib7....
If unfamiliar, CS50x Puzzle Day is an opportunity to collaborate on teams of 2, 3, and 4 to solve a packet of puzzles (i.e., logic problems). (Your team members don't need to have taken CS50x itself.)
See www.eventbrite.com/e/cs50x-puzz... for all details, including tickets. (Please forgive that space is limited!) Tickets available until 4pm on October 8, 2025. If ticket price would prevent you from attending, email outreach@cs50.harvard.edu.
🧩 The first-ever CS50x Puzzle Day in London is this Friday, October 10, 2025 at 5:00 PM British Summer Time, hosted at Meta by Professor David J. Malan, Professor Daniel Wilson, Professor Tom Crawford from Oxford, and CS50's alumni and friends at Meta.
Live from Harvard University at 1:30pm EDT, this is Week 5 of CS50 on data structures and more. Open to anyone online. This lecture will become part of CS50x 2026 on edX on January 1, 2026.
On YouTube at www.youtube.com/live/Sca41aX....
On Zoom at cs50.zoom.us/meeting/regi....
Live from Harvard University, this is Week 4 of CS50 (on memory and more). Open to anyone online. This lecture will become part of CS50x 2026 on edX on January 1, 2026.
On Zoom at cs50.zoom.us/meeting/regi....
On YouTube at youtube.com/live/aQFbviJ....
Live from Harvard University at 1:30pm EDT, this is Week 3 of CS50 on algorithms. Open to anyone online. (Or attend in person some day, per cs50.ly/attend.)
Watch on YouTube at youtube.com/live/4eN3_kb....
Register for Zoom at cs50.zoom.us/meeting/regi....
See www.eventbrite.com/e/cs50x-puzz... for all details, including tickets. (Please forgive that space is limited!)
CS50x Puzzle Day is an opportunity to collaborate on teams of 2, 3, and 4 to solve a packet of puzzles (i.e., logic problems). Puzzles are not programming challenges. No prior CS or programming experience needed, just logic and smarts! No team? No problem! We will help teams form at the event.
CS50 is back in the United Kingdom! Join us at Meta in London on Friday, October 10, 2025, for a CS50x Puzzle Day with Oxford Lifelong Learning, University of Oxford.
Taught over 12 weeks, this course teaches you how to solve problems, both with and without code, with an emphasis on correctness, design, and style. Topics include computational thinking, abstraction, algorithms, data structures, and computer science more generally.
Hello, world! CS50 will again be offered at University of Oxford in Michaelmas and Hilary terms. To attend online, register at lifelong-learning.ox.ac.uk/courses/intr....
Live from Harvard University at 1:30pm EDT, this is Week 2 of CS50 on arrays and more. Open to anyone online. (Or attend in person some day, per cs50.ly/attend.)
On YouTube at youtube.com/live/2Z-UFxZ....
On Zoom at cs50.zoom.us/meeting/regi....
Live from Harvard University at 1:30pm EDT, this is Week 1 of CS50 on C. Open to anyone online.
On YouTube at youtube.com/live/2Lg0W1_....
On Zoom at cs50.zoom.us/meeting/regi....
Or, to attend in person some day, see cs50.ly/attend.
• Artificial Intelligence on Friday, October 24, 2025, at 12:00 PM – 1:00 PM EDT
• HTML, CSS, and JavaScript on Monday, November 3, 2025 at 1:30 PM – 4:15 PM EST
• Flask on Monday, November 10, 2025 at 1:30 PM – 4:15 PM EST
• The End on Monday, November 17, 2025 at 1:30 PM – 4:15 PM EST
