This article presents an overview of the rapidly growing field of microwave devices? behavioral modeling, serving as an introductory overview to the two feature articles that follow it. Beginning with the distinction between behavioral and physics-based modeling, it provides an introduction to the under-lying theory of microwave device behavioral modeling, paving the way to the formulation of the most often used time-domain and frequency-domain model formats, whose details and applications are then explored in the other two articles of this special issue. Because behavioral modeling is, in its essence, a compact and systematic way of recording measured data and, from that, predicting similar behaviors, this article finally reviews the specific microwave measurement instruments necessary to extract the model parameters and validate the adopted model.