In the concluding chapter of his famous book on the theory of evolution by natural selection, Charles Darwin (1859) remarked that: When the views entertained in this volume on the origin of species, or when analogous views are generally admitted, we can dimly foresee that there will be a considerable revolution in natural history. This proved, of course, to be completely correct. At present there is a great divergence of opinion about the general importance of natural selection in the evolutionary process. Nevertheless, biologists are, on the whole, united in their acceptance of the potential power of selection in changing populations. Given this situation, it is not surprising to find that many attempts to detect the effects of natural selection have been made since the time of Darwin. This area of study has been called ecological genetics. It involves the collection of data of various kinds and, in many cases, the development of special methods for analysing these data. This book is a summary of methods for data analysis, concentrating on those that are applicable to animal populations, particularly wild populations.