Archaeogenetics is the research field of studying the genetic information contained in ancient DNA (aDNA) to gain insight into the past. Analysis of human aDNA from archaeological material has allowed archaeogeneticists to observe changes in the genetic composition of populations in an area through time. By using aDNA in this manner, a higher degree of resolution can be gained into the timing of past genetic transitions, compared to the resolution that is available when inferring the past from modern genomic data alone. In this thesis, I focus on the movement of genes, via migration of people and/or admixture, and the information that this movement can provide about human history. I introduce the differences between the inheritance mechanisms of uniparental (mitochondrial DNA and the Y-chromosome) and autosomal markers; the forces of evolution in population genetics; some methods commonly used in the analysis of human aDNA in the manuscripts included in this thesis; prior (archaeo-)genetics research regarding the population history of West Eurasia and the Americas -as context for my own research in these geographic areas-, and discuss the information gained by my own work about the population history of the areas studied, the limitations of archaeogenetic inferences, and the importance of combining archaeogenetic results with those from other disciplines when studying human history