Apolipoprotein (apo) B exists in two forms apoB100 and apoB48. ApoB100 is present on very low‐density lipoproteins (VLDL), intermediate density lipoproteins (IDL) and LDL. ApoB100 assembles VLDL particles in the liver. This process starts by the formation of a pre‐VLDL, which is retained in the cell unless converted to the triglyceride‐poor VLDL2. VLDL2 is secreted or converted to VLDL1 by a bulk lipidation in the Golgi apparatus. ApoB100 has a central role in the development of atherosclerosis. Two proteoglycan‐binding sequences in apoB100 have been identified, which are important for retaining the lipoprotein in the intima of the artery. Retention is essential for the development of the atherosclerotic lesion.