The field of palliative care in the United States developed in response to a public health crisis-namely, poor quality of life for patients with serious illness and their families-and most palliative care research to date has been appropriately focused on identifying patient and family needs and identifying gaps in the current health care system and in the education of our health care professionals. Research has also begun to develop and evaluate new interventions and systems to address these care gaps. Preliminary studies suggest modest benefits of an array of programs designed to deliver palliative care services. These benefits include improved pain and other symptoms, increased family satisfaction, and lower hospital costs. Unfortunately, the validity and reliability of these findings are limited by important methodological weaknesses including small sample sizes, poorly described and nongeneralizable interventions, diverse and nonstandardized outcome measures, and poor study designs (i.e., lack of appropriate control groups, nonblinded designs). Comprehensive and rigorous research is needed to evaluate the effect of well-delineated and generalizable palliative care structures and processes on important clinical and use outcomes. Large multisite studies that have adequate power to detect meaningful differences in clinical and use outcomes, and that use well-defined and generalizable structures and evidence-based care processes, well-defined uniform outcome measures, and analyses that link the outcomes of interest to individual components of the interventions, are needed to guide further development of the field.