Collecting information through surveys of a population is a common practice. This reference work outlines the mathematical and methodological foundations of survey research and provides a theoretical framework for evaluating its performance. It covers developments in sampling methods, estimation and adjustment techniques, and the tools needed to calculate the precision of the results obtained. Since, in the field of statistics, surveys constitute a relatively young discipline that has undergone significant development in recent years, this new edition has been extensively updated and expanded (by 250 additional pages!). In particular, it incorporates advances in: balanced sampling, indirect surveys, generalized calibration, handling nonresponse, repeated surveys over time, variance estimation in complex designs, surveys in small areas, etc. With a strong theoretical foundation, the book also emphasizes the interpretation of the main results of survey theory. It justifies field practice through these results, notably through the presentation of application cases. Its progressive approach makes it accessible to non-specialists with basic knowledge of descriptive and mathematical statistics: students, statistics professionals, users of survey results, as well as anyone wishing to acquire the basic techniques for designing and conducting surveys.