Cells cannot just go on dividing and dividing, otherwise there would be chaos. And, we would not be the beautiful people that we are. One of the main controls is called contact inhibition. When a few cells are placed in a dish in nutrient broth, the cells will divide until they have covered the bottom of the dish, then when they are all touching each other, cell division stops. The cells communicate with each other to end the division. There are also other controls called "go, no-go" switches. These are located along the path that the cell cycle takes, thus to continue or discontinue the process of cell division.