Studies where measurements are collected repeatedly on the same individual over time have received much attention in recent years. They are particularly popular in biomedical and health-care applications, where investigators are interested in identifying the influence of treatment on disease development. This is mainly due to their ability to characterize the change in the response variable over time and factors that affect the change. Longitudinal data is the process of collecting sample observations from a larger population over a given time period and the longitudinal study is the study in which subjects are followed over time to see their progress and change in the status. This means, in longitudinal studies we take repeated measurements of the same individual over a time span to encompass a detectable change in their disease/developmental status. Keeping the above points in view, this book has been written dealing with the Statistical Modeling and Analysis of Longitudinal data in Animal Sciences.