The mitogen-activated protein kinase (MAPK) family of kinases connects extracellular stimuli with diverse cellular responses ranging from activation or suppression of gene expression to the regulation of cell mortality, growth, and differentiation. The MAPK family has been studied extensively; however, the role of these kinases in cell growth and cell-cycle control has become increasingly complex. Patterns have begun to emerge from these studies that show the functions of MAPK subfamilies at different stages of the cell cycle. Their patterns of subcellular localization and movement during the cell cycle are subfamily-specific and have raised many questions about possible cell-cycle functions that have yet to be demonstrated. This article will compare and contrast our current understanding of the functions and localization patterns of the MAPK subfamilies (ERK, BMK, p38, and JNK) in cell-cycle control.