Eisosomes ('eis' meaning into or portal and 'soma', meaning body) are large, heterodimeric, immobile protein complexes at the plasma membrane which mark the site of endocytosis in some eukaryotes, and were discovered in the yeast Saccharomyces cerevisiae in 2006. Currently, seven genes: Pil1, Lsp1 and Sur7, Eis1, Seg1 and Ygr130C, Seg2, are annotated to the formation of the proteins identified in eisosomes. These organelle-like structures have put to rest the idea that sites of endocytosis in cells are chosen at random. Eisosomes have a profound role in regulating plasma membrane architecture and organization in yeast. Microscopic and genetic analyses link these stable, ultrastructural assemblies to the endocytosis of both lipid and protein cargoes in cells.