Cells are one of the cornerstones of the tissue engineering and regenerative medicine (TERM) paradigm and are ultimately responsible for producing the new tissue. Because of their regenerative potential, stem cells are central to TERM, where particular care is taken into recreating their natural niche, which regulates and modulates stem cell fate. Other cells used in TERM include differentiated cells or even cell lines for in vitro models. Growth factors and exosomes, which are both released by cells into the environment, can be incorporated into scaffolds to elicit desired responses in target cells. Cell sheet tissue engineering creates cell patches for clinical repair of various tissues. Chapter 4 offers a comprehensive overview of the cell element of the TERM paradigm.