How do researchers decide whose name comes first on a paper?

Question

Is it based on who contributed the most? How is this determined? Is it alphabetical? If so then someone with an A last name can contribute barely anything and everyone will still call it “Alberts et. al”

In: Other

Answer 1

The first author did most of the work, it was their project. Last author is the supervising professor or group leader. In between are contributors.