This chapter provides an overview of duration analysis, focusing on the specification and identification of duration models, particularly the Mixed Proportional Hazard (MPH) model and its extensions for multiple durations. The MPH model is widely used to describe the relationship between the empirical exit rate and background variables. However, since economic theories often do not lead to proportional specifications, the deep structural parameters of these theories need to be related to the reduced-form parameters. The chapter examines the specification and identification of the MPH model for single-spell and multi-spell data, and discusses the identification of multiple-duration models, where durations can be dependent through unobserved determinants. It also explores the issue of causal duration effects and selectivity. The chapter concludes with recommendations on empirical approaches and emphasizes the importance of additional data collection.This chapter provides an overview of duration analysis, focusing on the specification and identification of duration models, particularly the Mixed Proportional Hazard (MPH) model and its extensions for multiple durations. The MPH model is widely used to describe the relationship between the empirical exit rate and background variables. However, since economic theories often do not lead to proportional specifications, the deep structural parameters of these theories need to be related to the reduced-form parameters. The chapter examines the specification and identification of the MPH model for single-spell and multi-spell data, and discusses the identification of multiple-duration models, where durations can be dependent through unobserved determinants. It also explores the issue of causal duration effects and selectivity. The chapter concludes with recommendations on empirical approaches and emphasizes the importance of additional data collection.