The primary purpose of this paper is to introduce essential elements of cognitive information processing (CIP) theory, research, and practice as they existed at the time of this writing. The introduction that follows describes the nature of career choices and career interventions, and the integration of theory, research, and practice. After the introduction, the paper continues with three main sections that include CIP theory related to vocational behavior, research related to vocational behavior and career intervention, and CIP theory related to career interventions. The first main section describes CIP theory, including the evolution of CIP theory, the nature of career problems, theoretical assumptions, the pyramid of information processing domains, the CASVE Cycle, and the use of the pyramid and CASVE cycle. The second main section describes CIP theory-based research in examining vocational behavior and establishing evidence-based practice for CIP theory-based career interventions. The third main section describes CIP theory related to career intervention practice, including theoretical assumptions, readiness for career decision making, readiness for career intervention, the differentiated service delivery model, and critical ingredients of career interventions. The paper concludes with regularly updated sources of information on CIP theory. [This paper was produced by the Center for the Study of Technology in Counseling and Career Development, Florida State University. For "A Bibliography of Cognitive Information Processing Theory, Research, and Practice," see ED616622.]