Use of infrared detector arrays in astronomy began roughly 20 years ago, and our detection capabilities in parts of this spectral range have doubled about every seven months since then. A variety of approaches are now used for detector arrays operating from 1 μm to 1 mm and beyond. They include direct hybrid arrays of InSb and HgCdTe photodiodes that operate from 0.6 μm to 5 μm, and of Si:As impurity band conduction detectors from 5 μm to 28 μm; a number of approaches to photoconductive detector arrays in the far-infrared; and bolometer arrays read out by transistors or superconducting devices in the far-infrared through millimeter-wave spectral range. The underlying principles behind these approaches are discussed. The application of these principles is illustrated through detailed discussion of a number of state-of-the-art detector arrays.