Apoptosis is a form of intrinsic cellular suicide program,which is a wide physiological process in multicellular organisms and critical for the development,the cell senescence and the tissue homeostasis.The initial and progress of apoptosis is precisely regulated.This review will summarize current knowledge of the signal transduction pathways of apoptosis.Broadly speaking,there are three pathways in apoptosis: death receptor pathway,mitochondrion pathway and endoplasmic reticulum pathway.These ways can cross-talk and regulate apoptosis coordinately.