We summarize here a number of properties that have been described for G protein coupled membrane receptors. These concern structure-function relationship, regulation of expression and activity and linkage with pathology. The existence of subfamilies and subtypes is discussed in terms of evolution and selectivity. A comparison is made between binding sites for small ligands such as monoamines and larger ligands such as peptides and glycohormones. Cross-talk of G protein coupled receptors with receptor tyrosine kinase pathways is also discussed. Finally, the role of mutations in modulating receptor activity is evaluated with respect to human disease.