Blau syndrome is an autosomal dominant monogenic autoinflammatory disease characterized by a triad of skin rash, polyarthritis, and uveitis. It was first described in two distinct families by Edward Blau and Douglas Jabs in 1985 (Blau 1985; Jabs et al. 1985). In 2001, the condition was linked to single-gene mutations in the NOD2/CARD15 gene, establishing the genetic basis of Blau syndrome (Miceli-Richard et al. 2001). A sporadic form of the disease with the same phenotype was also identified and termed early-onset sarcoidosis (EOS) (Miceli-Richard et al. 2001). Similar to sarcoidosis, both Blau syndrome and EOS are chronic granulomatous conditions; however, they have significant differences in dominant clinical features. Patients typically present with noncaseating granulomas featuring epithelioid and giant cells, which are hallmark histologic findings (Iannuzzi et al. 2007). This chapter will review the clinical characteristics, pathophysiology, diagnosis, management, and prognosis of Blau syndrome.