Molecular abundances in AGB circumstellar envelopes

In this review the present status of molecules in circumstellar envelopes of AGB stars is presented. Emphasis is put on the determination of abundances, and estimates of their uncertainties, from an observational point of view. Despite an impressive number of circumstellar species detected, about 60, there remains much work before general conclusions can be drawn. In particular, sophisticated radiative transfer modelling of circumstellar line emission must be done. This requires a detailed knowledge of the stellar and circumstellar properties, as well as basic molecular physics data. Eventually, the full potential of circumstellar spectra can be used in the study of the central stars and the circumstellar medium.