Environmental issues such as global warming, ozone depletion and photochemical air pollution have increased concern about how pollutants affect the environment. This has led to an increased emphasis on detecting pollutants, understanding their sources of origin and measuring their concentrations in the environment. Laser-based detection methods are useful for these measurements; absorption spectroscopy can provide high detection sensitivity of many different species. The system designer has many alternatives when choosing semiconductor lasers and system configurations for spectroscopy applications. The price/performance trade-offs create myriad possibilities, each of which has advantages for specific applications. This article addresses the trade-offs among Fabry-Perot semiconductor lasers, external-cavity diode lasers and distributed feedback lasers and suggests ideal uses in research & development and commercial applications.