Fibrillin microfibril assembly is a cell regulated process, independent of tropoelastin. Distinct microfibril populations have been identified, suggesting that the cellular environment plays a role in regulating microfibril fate (Kielty et al. 2002). Fibrillin 1 may undergo limited assembly into dimers or trimers in the secretory pathway (Ashworth et al. 1999, Trask et al. 1999) but the formation of large microfibril polymers is extracellular. Microfibrils assemble close to the cell surface in a process that may require cell surface receptors. Fibrillins interact with several integrins (Sakamoto et al. 1996, Jovanovic et al. 2008) suggesting an assembly mechanism with similarities to fibronectin matrix formation. Heparan sulphate proteoglycans (HSPGs) and chondroitin sulfate containing proteoglycans (CSPGs) have also been proposed to have a role in assembly (Tiedemann et al. 2001). Fibrillin polymerization into fibres further requires the formation of disulfide bonds between fibrillins (Reinhardt et al. 2000), initially via calcium-binding epidermal growth factor domains at the C-terminus (Hubmacher et al. 2008), and transglutaminase cross-links (Kielty et al. 2002).