**Abstract**

Mesenchymal stem cell/stromal cells (MSCs) can differentiate into a variety of cell types, including osteocytes, adipocytes and chondrocytes. MSCs are present in the multiple types of adult tissue, such as bone marrow, adipose tissue, and various neonatal birth-associated tissues. Given their self-renewal and differentiation potential, immunomodulatory and paracrine properties, and lacking major histocompatibility complex (MHC) class II molecules, MSCs have attracted much attention for stem cell-based translational medicine research. Due to a very low frequency in different types of tissue, MSCs can be isolated and expanded *in vitro* to derive sufficient cell numbers prior to the clinical applications. In this chapter, the methodology to obtain primary bone marrow-derived MSCs as well as their *in vitro* culture expansion will be described. To assess the functional properties, differentiation assays, including osteogenesis, chondrogenesis and adipogenesis, 3-D culture of MSCs and co-culture of MSCs and tumor cells are also provided. Finally, the long-term culture associated alterations of MSCs, such as replicative senescence and spontaneous transformation, will be discussed for better understanding of the use of MSCs at the early stages for safe and effective cell-based therapy.

**Keywords:** Mesenchymal stem cell/stromal cells, primary culture, co-culture, 3-D culture, replicative senescence, spontaneous transformation
