Bacteria produce some lipids and lipid-related compounds that function as signals for intercellular communication among prokaryotes or even in inter-kingdom communication (i.e., between prokaryotes and eukaryotes). Most of these lipidic signals participate in quorum-sensing regulation, a process that is dependent on cell density and enables a coordinated response within the population. The number and variety of bacterial non-membrane lipids that have been found to function as molecular signals are increasing and include fatty acids, fatty acid esters, acyl-based molecules such as N-acylhomoserine lactones and γ-butyrolactones, alkyl-based compounds such as quinolones and dialkylresorcinols, and alkane-derived signals such as α-hydroxyketones. While most of these signals are amphipathic and can diffuse through membranes with some being volatile, the transport of more hydrophobic compounds is facilitated via outer membrane vesicles. Dedicated synthases are involved in the production of the different classes of lipidic signals, which are recognized by membrane-bound or cytosolic receptors that trigger specific signal transduction responses. These signals regulate important bacterial traits such as motility, production of antimicrobials, expression of virulence factors, and biofilm formation. In eukaryotic organisms, some of these bacterial lipids can affect development and immune responses.