Abstract: After briefly reviewing what we have learned about the neutrinos in the past 20 years, and explaining how we have learned it, we will focus on one of the leading open questions about the neutrinos: Are they identical to their antiparticles? We will explain why this question is so very interesting, why it is so devilishly difficult to answer, and how it might nevertheless be answered through future experiments. We will also discuss several potential consequences of the answer.