Squash commits into one with Git

Step 1: choose your starting commit

git rebase --interactive [commit-hash]

Where [commit-hash] is the hash of the commit just before the first one you want to rewrite from.

Step 2: picking and squashing

pick d94e78 Prepare the workbench for feature Z     --- older commit
s 4e9baa Cool implementation 
s afb581 Fix this and that  
s 643d0e Code cleanup
s 87871a I'm ready! 
s 0c3317 Whoops, not yet... 
s 871adf OK, feature Z is fully implemented      --- newer commit

[...]

Save the file and close the editor.

Step 3: Create the new commit

You have just told Git to combine all seven commits into the the first commit in the list. It's now time to give it a name: your editor pops up again with a default message, made of the names of all the commits you have squashed.