Natural selection and other evolutionary forces leave characteristic signatures in 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 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. We complement this with high-throughput experimental evolution in budding yeast, evolving thousands of lines simultaneously to explore the distributions of phenotypic changes and their correlations with the evolution of genetic variation within and between populations.