The requirements of infrared systems have increased significantly over the years, from the simple linear, low resolution, photoconductive array to the present-day, large area, high-density, photodiode (MIS and metalurgical) arrays, with on-focal-plane signal processing of considerable complexity. The success that has been achieved in meeting the performance goals appropriate for these systems has been due, to a large degree, to significant advances in the relevant materials technologies. The technologies of importance over the last twenty years are briefly reviewed, and the current state of the art, with its dominance by intrinsic alloy materials, is addressed in detail. The limitations of current bulk and epitaxial intrinsic materials technologies are considerable, both from a performance and a producibility point of view, when compared to the quality and quantity of material required by future infrared systems. These limitations are considered together with possible ways to overcome them.