The regionalization process that gives rise to the midbrain-hindbrain boundary. The midbrain-hindbrain domain of the embryonic brain is comprised of the mesencephalic vesicle and the first rhombencephalic vesicle at early somitogenesis stages. An organizing center at the boundary patterns the midbrain and hindbrain primordia of the neural plate. [ GOC:dph http://purl.obolibrary.org/obo/go/references/0000021 GOC:dgh GOC:cls GOC:jid GOC:isa_complete http://www.ncbi.nlm.nih.gov/pubmed/15541513 ]