Recent advances in understanding the cellular and molecular signaling pathways and global transcriptional regulators of adult mesenchymal stem cells have provided new insights into their biology and potential clinical applications, particularly for tissue repair and regeneration. This review focuses on these advances, specifically in the context of self-renewal and regulation of lineage-specific differentiation of mesenchymal stem cells. In addition we review recent research on the concept of stem cell niche, and its relevance to adult mesenchymal stem cells.