This chapter presents a state of the art summary of pituitary tumors relation to its biology, epidemiology, disease mechanisms, clinical signs, diagnosis, treatment and prognosis. Among tumors of the pituitary gland, pituitary adenomas are most common, while pituitary carcinomas may occasionally affect older people. Pituitary tumors, accounting for 10%–25% of all intracranial tumors, mainly occur in the fourth and seventh decades, with female preponderance. Differential diagnoses for pituitary adenomas and carcinomas include rare tumors/lesions that also occur at the suprasellar and sellar regions. Pituitary adenoma is composed of monomorphic cells with small, round nuclei, salt-and-pepper chromatin, and abundant cytoplasm without reticulin meshwork among tumors cells. Pituicytoma is a rare benign tumor derived from pituitcytes in neurohypophysis or pituitary infundibulum, possesses bland spindle cells in dense fascicles or storiform growth pattern, and stains positive for vimentin, S100 protein, and thyroid transcription factor-1; but, it is negative for neuroendocrine markers and pituitary hormones.