Cohomology is a powerful tool across many subfields of mathematics. There are a great many cohomology theories, so it is easy to lose track, and easy to get confused. In this talk I'll review the de Rham cohomology you'll have seen (perhaps a long time ago now) in the core geometry/topology course, before providing an overview of the derived functor cohomology, and a handwavey introduction to the sheaf cohomology that is fundamental to algebraic geometry. Hopefully time allows me to mention the étale, l-adic and crystalline cohomologies used in number theory, but this is very ambitious, so don't expect much detail!