One day last year, David Lippman got an interesting Google Alert. 1,300 miles away, fellow math professor James Sousa had created free video tutorials for almost every example question in David’s basic math textbook. James did all of that without asking for David’s permission: David had already given permission by licensing his work under a Creative Commons license.

David loves getting that kind of news. He’s dedicated his career to making it easier for instructors and students to get the math content they need. David licenses almost everything he creates under Creative Commons Attribution-ShareAlike, which allows anyone to republish, reuse, or remix a piece of content so long as they give him credit and share their own version under the same license. “Whatever I create’s not going to be perfect,” David says. “So I want to make sure that people have the ability to make changes and improvements, and hopefully contribute back.” —Team Open.