Data monitoring committees (DMCs) have become an increasingly common component of randomized clinical trials in recent years. As experience has accumulated, and more individuals and organizations have become involved in such activities, a variety of approaches to the operation of such committees has inevitably arisen. Because these committees play such a critical role in the process of new drug development, it is important to consider the implications of the different approaches that are being used. It is also timely to consider the present and possible future regulatory status of data monitoring committees. Published in 2001 by John Wiley & Sons, Ltd.