As precursors of wax compounds, very long chain fatty acids participate in the limitation of non-stomatal water loss and the prevention of pathogen attacks. They also serve as energy storage in seeds and as membrane building blocks. Their biosynthesis is catalyzed by the acyl-CoA elongase, a membrane-bound enzymatic complex containing four distinct enzymes (KCS, KCR, HCD and ECR). Twenty-one 3-ketoacyl-CoA synthase (KCS) genes have been identified in Arabidopsis thaliana genome. In this paper we present an overview of the acyl-CoA elongase genes in Arabidopsis focusing on the entire KCS family. We show that the KCS family is made up of 8 distinct subclasses, according to their phylogeny, duplication history, genomic organization, protein topology and 3D modelling. The analysis of the subcellular localization in tobacco cells of the different subunits of the acyl-CoA elongase shows that all these proteins are localized in the endoplasmic reticulum demonstrating that VLCFA production occurs in this compartment. The expression patterns in Arabidopsis of the acyl-CoA elongase genes suggest several levels of regulations at the tissular or organ level but also under stress conditions suggesting a complex organization of this multigenic family.