With the recent growth in interest in the terahertz region of the electromagnetic spectrum, there is a growing interest in laser sources for this area. There are many types of THz lasers including optically pumped, direct‐discharge, free‐electron lasers, THz quantum‐cascade lasers, and pulsed cyclotron resonance Ge lasers. This article will concentrate on the most common variety, optically pumped THz lasers, which, in‐turn, come in a number of versions including continuous wave (cw), pulse pumped, and cavity dumped. Within each of these categories, there are a large number of variations in cavity design and pump geometry. The present article will concentrate on the most ubiquitous of these, continuous‐wave optically pumped THz lasers.