Many attempts are underway for developing meeting support tools, but less attention is paid to the evaluation of meetingware. This article describes the development and testing of an instrument for evaluating meeting tools. First, we specified the object of evaluation-meetings-by means of a set of input, process, and outcome factors. Then, we designed the process of evaluation, consisting of, first, the generation of meeting behavior in the form of a controlled series of meetings within the context of a project and, second, the measurement of the identified meeting factors. To measure these factors, a rating scale, questionnaires, and information flow analysis were used. Next, the instrument was tested, and the factors for successful meetings were determined in 13 projects in which four participants had to meet four times. The evaluation instrument proved to be a reliable and useful aid for the development and improvement of meeting tools.