Cell culture is the process of growing cells in a controlled, in vitro environment in the laboratory. The cells can be either isolated directly from tissues or continued from previously cultured cell lines. Cells in cultures can be systematically studied, manipulated, and engineered. The development of cell culture (or tissue culture) has played a pivotal role in the progression of molecular biology and cell biology, as the vast amount of knowledge that we have today about cellular activities and functions comes from studies of cells in cultures. Cell culture has also become a fundamental part of biomaterials and bioengineering; for example, in biomaterials studies, we use cultured cells to study cell-material interactions, and in tissue engineering, we use cultured cells to construct artificial organs.