This book describes statistical models and methods for the analysis of longitudinal data, with a strong emphasis on applications in the biological and health sciences. The technical level of the book is roughly that of a final year undergraduate or first year postgraduate course in statistics. The book divides naturally into three blocks. The first three chapters provide an introduction to the subject, and cover basic issues of design and exploratory analysis. Chapters 4, 5, 6, and 11 develop linear models and associated statistical methods for data sets in which the response variable is a continuous measurement. Chapters 7, 8, 9, and 10 are concerned with generalized linear models for discrete response variables. Appendix A gives a brief review of the statistical background assumed. This book is intended for statisticians - MSc students and researchers.