A One Health approach requires that nontraditional partners with differing mandates collaborate and communicate effectively. Barriers to such redefined relationships range from personality and institutional cultural and value differences to impediments that require changes in agency-specific policies. This article reviews interagency One Health collaborations, nationally and internationally. It presents a series of case studies that describe situations in which barriers were overcome, thus culminating in successful One Health outcomes. The case studies illustrate challenges, tipping points, and externally enabling factors that help institutionalize cross-bureaucratic working relationships. Likewise, the cases demonstrate the added value of taking a One Health approach to solving (or preventing) public health problems.