This volume provides an introduction to multilevel analysis for applied researchers. The term multilevel refers to a hierarchical or nested data structure, usually individuals within organizational groups, but the nesting may also consist of repeated measurements on individuals over time or individuals within clusters as in cluster sampling. The expression multilevel model or multilevel analysis is used as a generic term for all models for hierarchical or nested data. This book presents two types of multilevel models: the multilevel regression model; and a model for multilevel covariance structures. Despite the book being an introduction, it includes a discussion of many extensions and special applications.