Most MAPKs have a number of shared characteristics, such as the activation dependent on two phosphorylation events, a three-tiered pathway architecture and similar substrate recognition sites. These are the "classical" MAP kinases.  But there are also some ancient outliers from the group as sketched above, that do not have dual phosphorylation sites, only form two-tiered pathways, and lack the features required by other MAPKs for substrate binding. These are usually referred to as "atypical" MAPKs. It is yet unclear if the atypical MAPKs form a single group as opposed to the classical ones.
The mammalian MAPK family of kinases includes three subfamilies: 
# Extracellular signal-regulated kinases (ERKs)
# c-Jun N-terminal kinases (JNKs)
# p38 mitogen-activated protein kinases (p38s)
Generally, ERKs are activated by growth factors and mitogens, whereas cellular stresses and inflammatory cytokines activate JNKs and p38s.