Creative Commons just reached an exciting milestone. As of this week, there are four million Creative Commons–licensed videos on YouTube. That’s over forty years’ worth of footage to remix and reuse, all licensed under CC BY, the most permissive CC license.

One thing that makes this mass of CC-licensed content really exciting is that all four million of those videos can be imported into YouTube’s online video editor. By letting people remix and adapt videos without having sophisticated editing software or expertise, YouTube and CC are making it easier for anyone to build on the work of others. And that’s pretty cool.

In her guest blog post on the YouTube blog, CC CEO Cathy Casserly muses on what’s possible when YouTubers share their creativity:

Do you need a professional opening for your San Francisco vacation video? Perhaps some gorgeous footage of the moon for your science project? How about a squirrel eating a walnut to accompany your hot new dubstep track? All of this and more is available to inspire and add to your unique creation. Thanks to CC BY, it’s easy to borrow footage from other people’s videos and insert it into your own, because the license grants you the specific permissions to do so as long as you give credit to the original creator.

You can pass on the creative spirit when you publish your video, by choosing the option to license it under CC BY so that others can reuse and remix your footage with the YouTube Video Editor. This is where the fun really starts. Imagine seeing your footage used by a student in Mumbai, a filmmaker in Mexico City, or a music video director in Detroit. By letting other people play with your videos, you let them into a global sandbox, kicking off a worldwide team of collaborators. We all yearn to create and contribute — now you can join the fun, and open the door to collective imagination.