It has been twenty years now since the phenomenon of the pseudogap - an energy gap which exists above the superconducting transition temperature - was discovered in the cuprates. Despite two decades of effort, what this phenomenon really is, and what causes it, has yet to be resolved. In this talk, I will review recent work on this subject, including the nightmarish possibility that there are multiple pseudogaps. I will then offer some thoughts on what it implies about high temperature superconductivity.
Host: Lev Ioffe