This book describes the driving forces behind the evolutionary process at the molecular and genome levels, the effects of the various molecular mechanisms on the structure of genes, proteins, and genomes, the methodology and the analytical tools involved in dealing with molecular data from an evolutionary perspective, and the logic of evolutionary hypothesis testing. Evolutionary phenomena at the molecular level are detailed in a way that can be understood without much prerequisite knowledge of molecular biology, evolution, or mathematics. Numerous examples that support and clarify the theoretical arguments and methodological discussions are included.