Postoperative pain management is still insufficient, leading to major deficits, including patient suffering, impaired surgical recovery, long-term opioid intake, and post-surgical chronic pain. Yet, identifying the best treatment options refers to a heterogeneous outcome assessment in clinical trials, not reflecting relevant pain-related aspects after surgery, and therefore hamper evidence synthesis. Establishing a core outcome set for perioperative pain management of acute pain after surgery may overcome such limitations. An international, stepwise consensus process on outcome domains (“what to measure”) for pain management after surgery, e.g., after total knee arthroplasty, sternotomy, breast surgery, and surgery related to endometriosis, was performed. The process, guided by a steering committee, involved 9 international stakeholder groups and patient representatives. The face-to-face meeting was prepared by systematic literature searches identifying common outcome domains for each of the 4 surgical procedures and included break-out group sessions, world-café formats, plenary panel discussions, and final voting. The panel finally suggested an overall core outcome set for perioperative pain management with 5 core outcome domains: physical function (in terms of a condition-specific measurement), pain intensity at rest, pain intensity during activity, adverse events, and self-efficacy. Innovative aspects of this work were inclusion of the psychological domain self-efficacy, as well as the specific assessment of pain intensity during activity and physical function recommended to be assessed in a condition-specific manner. The IMI-PROMPT COS seeks to improve assessing efficacy and effectiveness of perioperative pain management in any clinical and observational studies as well as in clinical practice.