Biocontrol is an important management tool that utilizes one species (a biocontrol agent) to control another (a target host) and can be an effective approach for controlling populations of invasive species across broad spatial scales. Most strategies of biocontrol involve introducing or supplementing natural predator, herbivore, parasitoid, or pathogen populations to reduce populations of target hosts. A successful biocontrol program results in the suppression (but not eradication) of target host populations across the landscape by reducing host abundance, reproductive output, or vigor. Climate change is complicating biocontrol. Biocontrol agents must have a clear ecological and/or evolutionary relationship with their target host in order to control populations effectively and avoid impacting non-target species. Climate-induced changes in phenology (timing of life events), morphology (form/structure), movement/behavior, physiology, and reproduction/development may differently affect the survival, reproduction, and performance/efficacy of both biocontrol agents and their hosts. There are growing concerns that mismatches between how biocontrol agents and their hosts respond to climate change could alter the efficacy of current and future biocontrol programs.