A common practice in the programming world is to maintain a history of the changes made to a program. Over time the different versions of the program are maintained in a software repository where the programmer can retrieve prior versions to return to an older, working state of their program.

In the previous section we mentioned placing your notebook on GitHub. Git is a software repository in wide use. GitHub is an internet-based instance of Git. Once you have any software in Git it will automatically be versioned. The next time you update your notebook in GitHub. Git will take the current instance, store it as a version in your history, and place the new instance as the current—where anyone accessing your GitHub repository will see the latest version by default.