Protocadherins are a large family of cadherin-like cell adhesion proteins that are involved in the establishment and maintenance of neuronal connections in the brain. There are three protocadherin gene clusters, designated alpha, beta and gamma, all of which contain multiple tandemly arranged genes. These genes generate thousands of different protocadherin proteins through alternative promoter usage and cis-alternative splicing. PCDHA and PCDHG family members form oligomers, which also increases the diversity of PCDH proteins at the cell surface. All three gene clusters, PCDHA, PCDHB, and PCDHG show upregulated expression during brain development, and PCDHA is subsequently downregulated by myelination. Expression of all three clusters continues in the olfactory bulb, hippocampus and cerebellum until adulthood. Members of the PCDH family are potential targets in schizophrenia and bipolar disorder pathogenesis. PCDHA10 produces at least three isoforms by alternative splicing.