Natural selection and other evolutionary forces leave characteristic signatures on the genetic variation within populations. My group uses a combination of theoretical and experimental approaches to study how this genetic variation is created and maintained, and to develop methods to infer the evolutionary history of populations from the variation observed in sequence data. Our focus is primarily on the dynamics and population genetics of natural selection in asexual populations such as microbes and viruses. We are developing new approaches to population genetic theory to better understand the structure of genetic variation in these populations. To complement this theoretical work, we have developed high-throughput techniques which allow us to directly observe the evolution of thousands of experimental budding yeast populations simultaneously, tracking changes in fitness and other phenotypic characteristics and correlating these with the evolution of genetic variation within and between populations.