The human body contains many specialized tissues that are capable of fulfilling an incredible variety of functions necessary for our survival. This volume in the Human Cell Culture Series focuses on mesenchymal tissues and cells. The in vitro study of mesenchymal cells is perhaps the oldest form of human cell culture, beginning with the culturing of fibroblasts. Fibroblasts have long been generically described in the literature, arising from many tissue types upon in vitro cell culture. However, recent studies, many enabled by new molecular biology techniques, have shown considerable diversity in fibroblast type and function, as described within this volume. Mesenchymal tissue types that are described within include bone, cartilage, tendons and ligaments, muscle, adipose tissue, and skin (dermis). The proper function of these tissues is predominantly dependent upon the proper proliferation, differentiation, and function of the mesenchymal cells which make up the tissue. Recent advancements in primary human mesenchymal cell culture have led to remarkable progress in the study of these tissues. Landmark experiments have now demonstrated a stem cell basis for many of these tissues, and, furthermore, significant plasticity and inter-conversion of stem cells between these tissues, resulting in a great deal of contemporary excitement and controversy. Newly-developed mesenchymal cell culture techniques have even lead to novel clinical practices for the treatment of disease.