When contract research organizations (CROs) were first formed, pharmaceutical companies outsourced to them only certain aspects of the conduct of their clinical trials. At first CROs were highly specialized entities, providing, for example, either biostatistical advice, clinical research associates who monitored investigational sites for regulatory compliance, or regulatory support. Gradually, full service CROs emerged, offering a full range of services for clinical trials, including the selection of investigators and investigational sites, assistance with patient recruitment, safety surveillance and reporting, site audits, and data management and biostatistics. This evolving relationship between CROs and the pharmaceutical and medical device industries has resulted in CROs assuming more and more of the regulatory and ethical risks and responsibilities inherent in the conduct of clinical trials. In this full service role, CROs, unlike sponsors, are not interested in the outcome of study, but like sponsors, are subject to heavy regulation by the federal government, must follow applicable state laws, must respect international guidelines, and are obliged to follow their own operating procedures. Moreover, they are judged by the industry on the basis of the scope and quality of services provided, including the degree of adherence to the research protocol, regulatory requirements, and timelines; the quality of the professional working relationships with investigators and institutions, both academic and community-based; and the validity of the data. Further, CROs are subject to comprehensive audits by sponsoring companies, FDA, and other regulatory authorities. For all these reasons, CROs are being tasked with strict vigilance of all stages of the clinical trial process to ensure that the laws, regulations, and industry standards designed for the protection of human subjects and data integrity are maintained.