During the past ten years, numerous reports have demonstrated the pres
ence of homologous sequences repeated in different proteins. These mot
ifs, that share common structures, are called modules. The great diver
sity of secreted proteins and particularly of those found in the extra
cellular matrix can in fact be reduced to a relatively small number of
distinct modules. In this review, we underline the importance of modu
larity of extracellular matrix macromolecules in their supramolecular
assemblies and in their physiological roles. The modules from which a
particular protein is built up can be involved both in the structure o
f the protein, acting for example as spacers, and in functionnal aspec
ts, leading to specific interactions with other extracellular proteins
or with specific membrane receptors. The resulting interactions accou
nt for the integrity of extracellular matrices. A mutation affecting a
single module can be responsible for a loss of function of the entire
protein. This can lead to severe heritable disorders.