This document provides an overview of empirical software engineering. It begins with an introduction to the need for empirical studies in software engineering to systematically evaluate human activities. The document then covers basic concepts like measurement, data collection, and analysis. It discusses empirical strategies like surveys, case studies, and controlled experiments. The document also outlines the process for conducting an empirical study and current tools. It concludes by examining the state of the art in empirical software engineering and opportunities to better integrate experimental results.