Currently >50 proteins have been reported to be associated with focal contacts and related ECM adhesions. Most of these contain multiple domains through which they can interact with different molecular partners, potentially forming a dense and heterogeneous protein network at the cytoplasmic faces of the adhesion site. The molecular and structural diversity of this 'submembrane plaque' is regulated by a wide variety of mechanisms, including competition between different partner proteins for the same binding sites, interactions triggered or suppressed by tyrosine phosphorylation, and conformational changes in component proteins, which can affect their reactivity. Indeed, integrin-mediated adhesions can undergo dynamic changes in structure and molecular properties from dot-like focal complexes to stress-fiber-associated focal contacts, which can further 'mature' to form fibronectin-bound fibrillar adhesions. These changes are driven by mechanical force generated by the actin- and myosin-containing contractile machinery of the cells, or by external forces applied to the cells, and regulated by matrix rigidity.