The overall lipid composition of cell membranes is defined by variations in the concentration of hundreds of individual species. Although, in principle, the unconstrained variations of lipid levels are able to generate infinite combinations of lipid composition, the action of regulatory circuits restricts the spectrum of possible lipid configurations in a given cell and under given conditions. Lipid configurations can be seen as a finite number of states that represent local energetic minima of the lipid compositional landscape. Thanks to their interplay with cell signalling, these configurations then promote the establishment of specific transcriptional programmes and of cell phenotypic states. In addition, the stability of lipid configurations allows them to be maintained over time and thus to propagate phenotypic states across cell generations. To reflect their properties of singularity and heritability, we have referred to these lipid configurations as lipotypes.