Mononuclear cellsMononuclear cells (MNCsMNCsMononuclear cells) derived from bone marrowMononuclear cellsderived from bone marrow and umbilical cord bloodMononuclear cellsderive from umbilical cord blood have emerged as promising candidates for regenerative medicine due to their unique biological properties and diverse therapeutic potential. This chapter provides a comprehensive overview of the cellular components within these MNC populations, including stem and progenitor cells, immune cellsImmune cells, and various subpopulations that contribute to their regenerative capabilities. The chapter also reviews the underlying mechanisms by which these cells exert their effects, focusing on their roles in modulating inflammation and immune responses, enhancing angiogenesisMechanisms of actionangiogenesis, providing neuroprotectionMechanisms of actionneuroprotection and promoting neurogenesisNeurogenesis, and facilitating tissue repair. Furthermore, the chapter highlights the clinical applications of bone marrow and umbilical cord bloodCord blood-derived MNCs, detailing indicationsIndications, optimal cell dosesCell therapydoses, timing of administration, routes of delivery, potential side effectsSide effects and complicationsComplications, and therapeutic effectivenessEffectiveness in treating neurological, cardiovascular, metabolic, and pulmonary diseases. In addition, the chapter discusses the challenges and future directions in harnessing these cells for clinical applications, emphasizing the need for standardized protocols and further research to optimize their efficacy and safetySafety in clinical settings.