Infrared zoom lens systems have benefited from advances in the state ofthe art during the past decade. These advances have included extending the zoom range, improvements in performance, reduction of size and weight, and minimizing complexity. The application of these developments to infrared zoom lens design is presented. The zoom lens systems of several companies active in the field are reviewed, with some reference to tolerancing techniques for production. Innovative reflective zoom systems are also considered. Promising future developments are discussed.