**Abstract**

Pheochromocytomas and paragangliomas are rare neuroendocrine tumors, with genetic background in about 40% of cases, involving more than 30 susceptibility genes. The susceptibility genes can be divided into three main molecular clusters: pseudohypoxic, kinase signaling, and Wnt signaling. Biochemical characterization of these particular tumors should be integrated into the diagnostic algorithm because it can help apply personalized medicine principles and targeted therapy. These tumors can present with very different genotype-phenotype correlations, and their characterization can help the clinical practitioner make optimal clinical management decisions and prioritize genetic testing. This chapter summarizes the most important aspects of genetics and clinical characteristics, together with new genotype-phenotype correlation data.

**Keywords:** pheochromocytomas, paragangliomas, genotype-phenotype correlations
