 The discussion below is structured as follows. Section 1 briefly outlines the origins of population genetics, focusing on major themes and controversies. Section 2 explains the Hardy-Weinberg principle, the starting point of much population-genetic analysis. Section 3 outlines some elementary models in population genetics and their consequences. Section 4 discusses random drift (the chance fluctuations in gene frequency that arise in finite populations), and coalescence (the joining up of gene lineages as we trace them back in time). Section 5 discusses the status of population genetics in biology. Section 6 examines some of the philosophical issues raised by population genetics.