The family of phosphoprotein phosphatases includes enzymes that dephosphorylate serine, threonine (EC 3.1.3.16) and tyrosine (EC 3.1.3.48) residues within their substrates. Analogous to kinases, some show certain specificity towards Ser/Thr or Tyr residues, like PPM1D (EC 3.1.3.16). Phosphatases that do not show this selectivity are classified as dual-specificity phosphatases (DUSP).DUSPs have been implicated as major modulators of critical signaling pathways that are dysregulated in various diseases. DUSPs can be divided into six subgroups on the basis of sequence similarity. Of these subgroups, a great deal of research has focused on the characterization of the mitogen-activated protein kinase phosphatases (MKPs). While DUSP1 has been identified as a prototypic MAPK phosphatase, an essential endogenous regulator of the inflammatory response to lipopolysaccharide (LPS), the DUSP6 functions as a feedback regulator of fibroblast growth factor (FGF) signaling to limit the activity of extracellular signal–regulated kinases (ERKs) 1 and 2.