In order to understand the function of the cell, which is the basic unit of human organism, the fundamentals of cell replication should be elucidated. Cell cycle checkpoints work in balance during the cell division process. The most important step in cell replication is to copy its own genetic material. During replication, mitosis lasts only I hour whereas 95% of the cell cycle process comprises the interphase. G1, S, G2 and M phases of the cell cycle are strictly controlled by the cell itself. Cell cycle checkpoints are sensitive to and control the errors that occur during the replication process, misegregation of the chromosomes, errors in DNA replication and any other errors that can occur during replication, thus maintaining the cell cycle. The molecules that have a role in the cell cycle and mitosis such as MPF (maturation promoting factor), cyclines and cell cycle inhibitors have very important functions, and proper maintenance of the cell cycle depends on the interaction between them. On the other hand, interaction between the different growth factors and cyclins during the switch to silent phase, the cell cycle inhibitors (p21 and TGF-beta) during the termination of the cell cycle, and the tumor suppressor genes (p53 and Rb) have major roles in the maintenance of the cell cycle. DNA packaging, chromosome condensation, formation of mitotic spindle and cytokinesis are under control during mitosis. In this review, the steps in mitosis and meiosis, the control points and the functions of major modulator molecules during the cell cycle are broadly reviewed with referral to recent findings.