This review provides an overview of the current understanding of adult mesenchymal stem cells (MSCs), focusing on their existence, biological niche, self-renewal potential, multilineage differentiation potential, and regulatory mechanisms. MSCs are considered promising candidates for cell-based therapies due to their ability to self-renew and differentiate into various mesenchymal lineages. However, the precise identity and molecular mechanisms governing their stem cell potential remain largely unknown. The review discusses the challenges in identifying MSCs in vivo and the methods used to isolate and characterize them, including the colony-forming unit-fibroblast (CFU-F) assay. It also explores the concept of the MSC niche, which supports hematopoietic and mesenchymal stem cells in bone marrow. The review highlights the heterogeneity of MSCs and their potential for transdifferentiation and dedifferentiation, emphasizing the need for further research to understand the molecular and cellular mechanisms underlying these processes. Additionally, it reviews the application of MSCs in cell and gene therapy, including the use of viral and non-viral gene delivery methods, and the challenges of expanding MSCs for clinical use. The conclusion underscores the importance of understanding the regulation of MSC maintenance and differentiation to optimize their therapeutic potential.This review provides an overview of the current understanding of adult mesenchymal stem cells (MSCs), focusing on their existence, biological niche, self-renewal potential, multilineage differentiation potential, and regulatory mechanisms. MSCs are considered promising candidates for cell-based therapies due to their ability to self-renew and differentiate into various mesenchymal lineages. However, the precise identity and molecular mechanisms governing their stem cell potential remain largely unknown. The review discusses the challenges in identifying MSCs in vivo and the methods used to isolate and characterize them, including the colony-forming unit-fibroblast (CFU-F) assay. It also explores the concept of the MSC niche, which supports hematopoietic and mesenchymal stem cells in bone marrow. The review highlights the heterogeneity of MSCs and their potential for transdifferentiation and dedifferentiation, emphasizing the need for further research to understand the molecular and cellular mechanisms underlying these processes. Additionally, it reviews the application of MSCs in cell and gene therapy, including the use of viral and non-viral gene delivery methods, and the challenges of expanding MSCs for clinical use. The conclusion underscores the importance of understanding the regulation of MSC maintenance and differentiation to optimize their therapeutic potential.