The primacy of research for social work has been long and widely recognized. Nearly two years ago this journal's editorial characterized research as the profession's most pressing need and underscored the importance of studies that could shed light on works (Fortune & Proctor, 2001). Although the quality and quantity of social work research has steadily increased, tests of the effectiveness of interventions remain too rare in this and other journals. Given the rigor and resource requirements of studies, their number is unlikely to increase dramatically in the immediate future. Yet, social work has a pressing need for knowledge. While we wait and while we work to increase studies, is important to consider how other kinds of research can inform the development and testing of interventions. The pace of development can be accelerated and the clinical appropriateness of new interventions enhanced by studies that, even though not actually testing a particular intervention, shed light on client needs, current practice, and service delivery systems. Research about practice, its challenges, its priorities, and its participants, has the potential to inform development and guide the application of existing interventions to new practice contexts. I characterize such research as intervention informative research. What types of studies can be informative? First, we need studies that help determine the problems that are priorities for social work intervention. Studies that document problems are not new; social work has a long tradition of research on social problems, their prevalence, and rates among vulnerable groups. Such research remains important. But the existence of a problem, or a particular diagnosis, does not always indicate need for treatment (Spitzer, 1998). Rather, studies documenting problem rates will be more helpful if they are shaped by the needs of development. The critical question for development is whether a problem warrants social work intervention. Thus, research needs to help us better understand problem severity, duration, variability over time, costs, and consequences for social and interpersonal functioning. Also important are clinical epidemiological studies that document problem prevalence among the clients served by social services agencies. For example, what are the rates of mental disorder, substance abuse, or domestic violence among social services clients? For many clients in social services agencies, social workers may be the first--or only--source of detection and help for such problems. Clinical epidemiological studies documenting the prevalence of such problems can inform treatment priorities and assessment protocols. Epidemiological and clinical epidemiological studies can be informative. Few social workers could name a client who has, or presents for help, only one problem. Most social work clients experience multiple problems, often of sufficient severity and complexity that they pose for time, attention, and resources (Klinkman, 1997). As resources for agencies and programs shrink, interventions must focus on the most pressing of problems among competing demands. For example, when clients experience an array of pressing problems such as abuse, food insufficiency, and housing instability, concerns such as depression or substance abuse may not be priorities for assessment and treatment. Research is needed that helps clarify the nature, extent, and consequences of competing demands from the perspectives of providers, program administrators, clients, and family members. In traditional efficacy research requiring the test of interventions under uniform and controlled conditions, clients with comorbidity or co-occurring problems are typically excluded to maximize internal validity. Efficacy studies will likely remain important in an iterative process of knowledge development, but social work ultimately requires studies that test interventions in relation to real-world contexts, with maximum external validity. …