The present invention provides substituted imidazo[1,2-b]pyridazine derivatives, pharmaceutically acceptable salts thereof, and tautomers of any of the foregoing, where such compounds inhibit β-site amyloid precursor protein-cleaving enzyme (BACE), which may be useful in the treatment of diseases in which BACE is involved, such as Alzheimer's disease. The invention also provides pharmaceutical compositions comprising any of these compounds and the use of any of these compounds and compositions in the treatment of diseases, disorders, or conditions in which BACE is involved.