Since the original description of McCune Albright syndrome, the clinical spectrum of fibrous dysplasia, café au lait marks and precocious puberty has been enlarged to include multiple features within an individual or forme fruste of the disorder. This review serves as an introduction to a more detailed analysis of individual organ involvement in later papers. Recent insights into molecular pathways and recognition of overlap between clinical syndromes and signaling pathways of embryonic cellular differentiation, growth and function of many tissues, has improved understanding of this complex disorder. The article touches briefly on the underlying stimulatory G protein mutations with their mosaic distribution in tissues. Fibrous dysplasia, associated malignancies and endocrinopathies are discussed, including gonadotrophin independent precocious puberty in females and males, thyroid disease, acromegaly and Cushing syndrome. Café au lait marks are an overlapping feature seen in other signaling disorders. Their management is discussed.