Osteoclasts are highly specialized cells, derived from the hematopoietic lineage, that resorb mineralized bone matrix. Osteoclast precursors can be recruited to the bone remodeling sites by specific cytokines in the microcellular environment, including some secreted by osteoblasts, fibroblasts, and osteocytes. In this book, the authors present current research in the study of the morphology, functions and clinical implications of osteoclasts. Topics include osteoclast formation and function and its risk in skeletal bone disease; the high osteoclastogenic potential of human osteosarcoma cells; osteoclast biology regarding Paget’s disease and p62 mutations; the role of immuno-skeletal interface in the regulation of osteoclast formation; and osteoclasts in patients with neurofibromatosis 1.