The chapter discusses the role of mitogen-activated protein kinase (MAPK) pathways in regulating various cellular processes such as cell proliferation, differentiation, and death. MAPK modules consist of three sequentially activated protein kinases, initiated by specific extracellular cues. The activation process involves a MAPK kinase kinase (MAPKKK) and a MAPK kinase (MAPKK), leading to the activation of the MAPK by dual phosphorylation. Once activated, the MAPK phosphorylates substrates to modulate protein function and gene expression. MAPKs are categorized into three main families: ERKs (extracellular-signal-regulated kinases), JNKs (Jun amino-terminal kinases), and p38/SAPKs (stress-activated protein kinases). Each family has distinct motifs and functions. ERKs respond to growth factors and mitogens, JNKs to environmental stresses and inflammatory cytokines, and p38s to environmental stresses and inflammatory cytokines. These pathways involve specific scaffold proteins that enhance signaling efficiency and spatial regulation. The chapter also highlights the importance of these pathways in various biological processes and their roles in human diseases, providing a comprehensive overview of the structure and function of MAPK pathways.The chapter discusses the role of mitogen-activated protein kinase (MAPK) pathways in regulating various cellular processes such as cell proliferation, differentiation, and death. MAPK modules consist of three sequentially activated protein kinases, initiated by specific extracellular cues. The activation process involves a MAPK kinase kinase (MAPKKK) and a MAPK kinase (MAPKK), leading to the activation of the MAPK by dual phosphorylation. Once activated, the MAPK phosphorylates substrates to modulate protein function and gene expression. MAPKs are categorized into three main families: ERKs (extracellular-signal-regulated kinases), JNKs (Jun amino-terminal kinases), and p38/SAPKs (stress-activated protein kinases). Each family has distinct motifs and functions. ERKs respond to growth factors and mitogens, JNKs to environmental stresses and inflammatory cytokines, and p38s to environmental stresses and inflammatory cytokines. These pathways involve specific scaffold proteins that enhance signaling efficiency and spatial regulation. The chapter also highlights the importance of these pathways in various biological processes and their roles in human diseases, providing a comprehensive overview of the structure and function of MAPK pathways.