N-Acyl homoserine lactones (Abbreviated as AHLs or N-AHLs) are a class of signaling molecules involved in bacterial quorum sensing, a means of communication between bacteria enabling behaviors based on population density.

The first AHL (N-3-(oxo-hexanoyl)-homoserine lactone) was found as the natural inducer of bioluminescence in the bacterium Vibrio fischeri. Quorum sensing by the means of AHLs contributes to regulate the transcription of specific genes and therefore expression of specific phenotypes, including growth, virulence, biofilm formation, bioluminescence, production of exopolysaccharide (EPS). Over 50 Gram-negative bacteria species (including several pathogenic species) use AHLs as autoinducers and the means of their communication in Quorum sensing. in one study, AHL was shown to interact with eukaryotic cells, and mitigate an immune response and facilitates infection. AHLs are one of the major groups of the autoinducer (AI) molecules which are found primarily in Gram-negative proteobacteria but also in some bacteriodetes, cyanobacteria, and archaea. The other two major groups are oligopeptides AIs in Gram-positive bacteria; and autoinducer-2 (AI-2), as a universal signal for interspecies communications.