The book "Design of Observational Studies" by Paul R. Rosenbaum offers a comprehensive introduction to statistical inference and the principles that guide the design of observational studies. Observational studies are crucial when randomized experiments are unethical or impractical, and they are applied in various disciplines such as medicine, economics, epidemiology, education, psychology, political science, and sociology. The quality of the results of an observational study heavily depends on its design. This academic book is divided into four parts and addresses both theoretical and practical aspects of designing observational studies, including the use of propensity scores and analysis planning. It is aimed at professionals and students who wish to develop a deeper understanding of the methodology and challenges of observational studies.