Palliative medicine has only recently joined the ranks of evidence-based medical subspecialties. Palliative medicine is a rapidly evolving field, which is quickly moving to redress its historical paucity of high-quality research evidence. This burgeoning evidence base can help support the application of evidence-based principles in palliative and hospice clinical care and service delivery. New knowledge is generally taken into practice relatively slowly by established practitioners. At present, the translation of evidence into palliative and hospice care clinical practice lags behind emerging research evidence in palliative care at even greater rates for three critical reasons: 1) the application of research results to specific clinical subpopulations is complicated by the heterogeneity of palliative care study subpopulations and by the lack of a recognized schema for describing populations or services; 2) definitional issues in service provision are, at best, confusing; and 3) fundamental research concepts (e.g., external validity, effect size, generalizability, applicability) are difficult to apply meaningfully in palliative care. This article provides a suggested framework for classifying palliative care research subpopulations and the clinical subpopulations to which the research findings are being applied to improve the ability of clinicians, health planners, and funders to interpret and apply palliative care research in real-world settings. The framework has five domains: patients and caregivers; health professionals; service issues; health and social policy; and research.