Palliative care aims to improve the quality of life of patients and their families and reduce suffering from life-threatening illness. In assessing palliative care efficacy, researchers must consider a broad range of potential outcomes, including those experienced by the patient's family/caregivers, clinicians, and the health care system. The purpose of this article is to summarize the discussions and recommendations of an Outcomes Working Group convened to advance the palliative care research agenda, particularly in the context of randomized controlled trials. These recommendations address the conceptualization of palliative care outcomes, sources of outcomes data, application of outcome measures in clinical trials, and the methodological challenges to outcome measurement in palliative care populations. As other fields have developed and refined methodological approaches that address their particular research needs, palliative care researchers must do the same to answer important clinical questions in rigorous and credible ways.