The casein kinase 1 (CK1; EC 2.7.11.1) family of monomeric serine/threonine protein kinases is involved in many diverse and important cellular functions, such as regulation of membrane transport, cell division, DNA repair, circadian rhythms, and nuclear localization. Moreover, multiple CK1 family members have been implicated in both positively and negatively regulating Wnt and Hedgehog (Hh) signaling. No less than seven family members are currently recognized: α, β, γ1, γ2, γ3, δ, and ϵ. The family members appear to have similar substrate specificity in vitro, and substrate selection is thought to be regulated in vivo via subcellular localization and docking sites in specific substrates.CK1α, CK1δ, and CK1ε are all known to play roles in modulating circadian rhythms. CK1δ and CK1ε phosphorylate PER and trigger its proteosomal degradation; mutations in each affect the clock in vivo. Additionally, CK1δ plays an important role in vesicular trafficking, chromosome segregation, cell cycle progression, cytokinesis, and developmental processes. Indicative of potential roles in microtubule organization, CK1δ mediates neurite outgrowth and the function of brain-specific microtubule-associated proteins.Casein kinase 2 (CK2; EC 2.7.11.1) is a ubiquitous, highly pleiotropic and constitutively active Ser/Thr protein kinase, independent of either second messengers or phosphorylation events. It has been implicated in neoplasia, cell survival, apoptosis, and virus infection. CK2 consists of a tetrameric structure composed of two regulatory β-subunits and two catalytic units (α and α′) in a homomeric or heteromeric conformation. The enzyme is known to operate as phosphorylating agent for more than 300 substrates known to date. Like CK1 family members, CK2 activity has been reported to be implicated in the Wnt signaling pathway as well.