TANK-binding kinase 1 (TBK1) was identified as a binding partner for Optineurin (OPTN) in two-hybrid screens, an interaction confirmed by overexpression/immunoprecipitation experiments in HEK293 cells and by coimmunoprecipitation of endogenous OPTN and TBK1 from cell extracts. A TBK1 binding site was located between residues 1-127 of OPTN, residues 78-121 displaying striking homology to the TBK1-binding domain of TANK. The OPTN-binding domain was localised to residues 601-729 of TBK1, while TBK1[1-688] which cannot bind to TANK, did not interact with OPTN. The OPTN[E50K] mutant associated with Primary Open Angle Glaucoma (POAG) displayed strikingly enhanced binding to TBK1, suggesting that this interaction may contribute to familial POAG caused by this mutation.