Michael Hartl

Welcome to Michael Hartl’s home on the Web! You might know me as cofounder and principal author at Learn Enough, as the creator of the Ruby on Rails Tutorial, or as founder of Tau Day and author of The Tau Manifesto.

Learn Enough is a tech education company that produces books, videos, and online courses on web development and related subjects. Through Learn Enough, I’ve published over ten tutorial books and courses on topics such as the Unix command line, text editors, version control, HTML, CSS & Layout, JavaScript, and Ruby.

Learn Enough is an outgrowth of the Ruby on Rails Tutorial, which has been the leading introduction to web development with Rails since its launch in 2010. Once called his “favorite book” by Wikipedia founder Jimmy Wales, the print edition* of the Ruby on Rails Tutorial is a bestseller in its category and has earned over 450 5-star Amazon reviews through six editions. Like all the main Learn Enough tutorials, the Rails Tutorial is available as a book, video series, and self-paced online course.

I’m also (in)famous as the author of The Tau Manifesto, an influential math essay arguing that “pi is wrong”—the right number being $\tau\ \mathrm{(tau)} = C/r = 6.283185\ldots$ The Tau Manifesto’s introduction of $\tau$ as the “true circle constant” has had a significant impact on geek culture, including changing the time of day MIT announces its admissions decisions, being supported by Python, the Khan Academy, and the official Google calculator, and being covered in The Wall Street Journal. The Tau Manifesto is currently available in seven different languages, and its associated holiday, Tau Day, is celebrated annually on 6/28 by thousands of math nerds around the world.

My educational background is in physics, with a bachelor’s degree from Harvard and a Ph.D. from Caltech, where I studied black hole dynamics and was an award-winning instructor in theoretical and computational physics. I’m also an alumnus of Y Combinator, the entrepreneur program that has produced companies such as Reddit, Stripe, Coinbase, Dropbox, and Airbnb.

Other interests include reading old books, languages, physical fitness, and martial arts (including Krav Maga Level 5, a “black belt in self-defense”).