The Common Data Element (CDE) Dictionary is an online vocabulary repository sponsored by the National Cancer Institute (NCI). CDE, a unique language for cancer clinical trials, was developed to standardize the terminology utilized in such trials and to promote the uniform collection of study data. A Web-based dictionary was created to collect and store these data terms. To create the CDE Dictionary, a collaborative effort was initiated by NCI with experts in a variety of oncology-related disciplines from clinical trials' cooperative groups, along with other trialists to develop the terminology used to collect information specific to cancer clinical trials. Terms and values associated with CDEs were chosen based on established standards. Each data element was reviewed to see how it could best be represented in an electronic data collection. The Cancer Therapy Evaluation Program (CTEP) has implemented the use of CDEs in the development of the case report forms (CRFs) that are used for the collection of clinical trial data on national Phase-3 trials authored by the clinical trials' cooperative groups. All CRFs are reviewed in CTEP to assess the usage of the CDEs. A change management process has been developed for both the content and the database architecture to provide a robust yet stable structure for the dictionary. This process will also enhance the procedure for submission of new additions to the dictionary and harmonize suggested changes to currently available CDEs. The goal is to maintain a common nomenclature across modalities and diseases whenever possible, to provide consistency in the CDE terminology.