Comprehensive geriatric assessment (CGA) is a multidimensional interdisciplinary diagnostic process focused on determining a frail elderly person's medical, psychological, and functional capabilities in order to develop a coordinated and integrated plan for treatment and long-term follow-up. Geriatrics interventions building on CGA are defined from their historical emergence to the present day in a discussion of their complexity, goals and normative components. Through literature review, questions of the effectiveness and costs of these interventions are addressed. Evidence of effectiveness is derived from individual trials and, particularly, recent systematic reviews. While the trial evidence lends support to the proposition that geriatric interventions can be effective, the results have not been uniform. Review of meta-regression studies suggests that much of this outcome variability is related to identifiable program design parameters. In particular, targeting the frail, an interdisciplinary team structure with clinical control of care, and long-term follow-up, tend to be associated with effective programs. Answers to cost-effectiveness questions also vary and are more rare. With some exceptions, existing evidence as exists suggest that geriatrics interventions can be effective without raising total costs of care. Despite the attention given to these questions in recent years, there is still much room for clinical and scientific advance as we move to better understand what CGA interventions do well and in whom.