The cell envelope of pathogenic mycobacteria is highly distinctive in that it contains a number of lipids esterified with structurally related long-chain multi-methyl-branched fatty acids. These lipids have long been thought to play important roles in the cell envelope structure as well as in the pathogenicity of the tubercle bacillus. This review summarizes what is known about the biosynthesis of long-chain multiple methyl-branched fatty acid-containing lipids in Mycobacterium tuberculosis and describes the most recent findings about their regulation, transport across the different layers of the cell envelope and their biological functions.