Neuroendocrine tumors (NETs) comprise a wide range of neoplasms with diverse biological behaviors, often secreting excessive amounts of endocrine-active substances causing hormone syndromes. They are classified according to the location of the primary site and the level of histological differentiation, which has prognostic as well as therapeutic implications. Biotherapy had traditionally a significant role in the treatment of these tumors, when not amenable to surgery or local treatments. Control of carcinoid syndrome with somatostatin analogs (SSAs) significantly contributed to the improvement of the quality of life. Also, interferon has long been administered, but data were based on small studies. In contrast, PROMID and CLARINET randomized phase III trials provided the first strong evidence of significant improvement in progression-free survival in patients with gastroenteropancreatic (GEP)-NETs with octreotide and lanreotide, respectively, validating somatostatin receptors as important targets. Clinical trials testing the role of these SSAs in other primaries, e.g., lung carcinoids, as well as the efficacy of newer analogs are underway.