Most protein kinases contain a conserved catalytic domain belonging to the eukaryotic protein kinase (ePK) superfamily (all other protein kinases are classified as atypical protein kinases, or aPKs). ePKs are classified into 7 major groups, and are subdivided into families, and sometimes subfamilies, based on the sequence of their ePK domains. To look at the structure of the groups, here are alignment and phylogenetic trees for the major groups. Alignments may be viewed with programs such as ClustalW, BioEdit or Belview; Trees may be viewed with programs such as TreeView or HyperTree. The tree.pdf files are one-page images of the trees in Adobe Acrobat format.