M odern signal processing and control algorithms are invariably implemented digitally, yet most real-world systems evolve in continuous time. Hence, the interaction between sampling and the behavior of continuous-time systems is an important ingredient in all real-world signals and systems problems.The literature on sampled-data systems goes back several decades [1]- [5]. Modern systems allow much faster sampling rates than were previously possible, which suggests that it is timely to reexamine sampled-data models [6]- [8]. Such a re-examination is the main goal of this article. A tutorial overview is provided of several related topics, including » exact and approximate sampled-data models arising from an underlying continuous-time system » connections between sampled-data models and the underlying continuous-time systems at fast sampling rates » intersample behavior.