The ejecta of evolved stars are excellent chemical laboratories where a large variety of exotic molecular species are formed in situ. Molecules are detected in the circumstellar material of almost every type of evolved star, no matter if it is a low-mass or massive star. These types of evolved stars comprise Asymptotic Giant Branch (AGB), post-AGB (planetary nebulae), red supergiant, yellow hipergiant, luminous blue variable, Wolf-Rayet, and supernovae. However, the largest variety and complexity of molecules is found in the nearly isotropic expanding envelopes around AGB stars. The gentle stellar wind developed during this phase possesses ideal conditions to trigger the formation of dust particles and favor the synthesis of different types of molecules.

Carbon-rich stars AGB stars still surpass oxygen-rich AGB stars in the number and complexity of molecules detected, with IRC+10216 being the richest molecular laboratory among these types of objects and even among any type of astronomical source. Around half of the molecules known in space are observed toward this C-star envelope.

Recent times are seeing a significant progress in this area because the increased frequency coverage and the improved sensitivity of telescopes is allowing to discover new circumstellar molecules, but also because the order-of-magnitude enhancement in spatial resolution of ALMA and NOEMA is making possible to pinpoint the exact chemical origin of each type of molecule in these environments. These observations are leading to a change of paradigm in our understanding of how the chemistry works in envelopes around AGB stars.

In this talk I will review the status concerning molecular complexity around evolved stars, and I will also briefly discuss the prospects for the future.