Perhaps one of the most useful tools in SharePoint is its Version History capability, which provides a running list
of all changes that have occurred in your files over their lifetimes.

Each time a file is changed a snapshot is automatically taken and permanently stored (up to 500 versions!). Not
only can you view the list to see who edited the file and when, but you can view any of these previous versions
with a single click of the mouse. Version History can be accessed two ways: