Cell differentiation is a programed process of gene regulation, by which lineage-specific genes of stem cells or progenitor cells are activated (Wu, 2011a). On the other hand, the opposite process, called cell reprogramming, enables the differentiated cells to become stem cells and reacquire pluripotency (Wu, 2011b). In the present issue, four research articles report novel biological and chemical factors that can be used for controlling the processes of particular cell differentiation or reprogramming. These findings might provide new tools for generating pluripotent stem cells or regulating cell differentiation.