Conservation biological control suppresses pests by promoting established rather than inoculative or mass released natural enemies. Research in this approach has expanded rapidly this century but uptake remains limited. Why? Most of the 150 peer reviewed papers reporting field experiments include results on natural enemies and/or pests. Only a minority report effects on crop damage levels or yield, and very few consider economic consequences. This is despite evidence for potential benefits across this full spectrum of response variables. We argue that the limited scope of work to date constrains the development of a compelling evidence base to demonstrate the field effectiveness of conservation biological control, hampering its uptake so encourage researchers to include the assessment of economic impact in future studies of conservation biological control. This article is protected by copyright. All rights reserved.