An overview of acoustic wave sensors for gas sensing is presented from both a fundamental and a practical point of view. The main interaction mechanisms between the acoustic wave and gaseous species are briefly reviewed, followed by a descriptive survey of the different types of sensors. Detailed results for the sensitivity of different acoustic modes are presented with numerical examples for realistic cases. A critical discussion is given of several approaches to chemical selectivity and the many practical issues of importance for environmental sensing. Anticipated future trends are presented in the conclusion. (C) 1999 Elsevier Science S.A. All rights reserved.