The coordination of the processes of cell proliferation, growth and differentiation in a multicellular organism - that is, the organism, or system control - is a prerequisite for normal development. Violation of system control mechanisms causes uncontrolled proliferation of cells, which leads to tumor growth. The system control of cell proliferation in higher plants has been studied much worse than in animals, largely because plants form tumors much less frequently than animals. Such "stability" of plants to tumor growth is connected with greater "reliability" of mechanisms of systemic control of cell proliferation in plants, which, despite a number of similarities, have a fundamentally different organization than in animals. In this book, we tried to present modern concepts of different levels of control of cell proliferation in higher plants, as well as describe the most studied cases of tumor development in plants in terms of mechanisms of systemic control.