Everyone has heard about "free software" and "open source", but what those terms actually mean is not always very clear, even for people that produce software. First of all, I will briefly explain those terms, and the reader will see that the open source philosophy has many ideas in common with Science. Then, I will define what I mean by "academic software" and I will present some arguments in order to show that Science would benefit a lot if scientists that produce software released them as open source