Before we delve any further into our study of molecular evolution, it's probably useful to back up a bit and talk a bit about the types of data that are available to molecular evolutionists. We've already encountered a several of these (AFLPs, microsatellites, and SNPs), but there are a variety of important categories into which we can group data used for molecular evolutionary analyses, and it's useful to remind everyone what those groups are and to agree on some terminology for the ones we'll say something about. Let's talk first about the physical basis of the underlying data. Then we'll talk about the laboratory methods used to reveal variation.