Compared to the concept of interpersonal deliberation, little is known about the underlying and preceding cognitive processes of citizens' deliberative discussions. The aim of this article is to develop a psychometric measurement for these processes, which—following an idea advanced by Goodin ()—may be called “deliberation within.” The measurement is constructed based on theoretical definitions of the concept and further normative criteria of citizen deliberation. In three empirical studies using independent samples, the psychometric properties of the measurement are assessed, and evidence for its reliability as well as structural and criterion validity is offered. The resulting scale may serve as a useful instrument not only for deliberation research, but also for further communication research related to political processes.