The mailed questionnaire research process developed historically as part of the survey research movement, with guidelines and models drawn from an array of scientific research methods and disciplines. Although the mailed questionnaire has become one of the most popular research instruments for obtaining data beyond the reach of the observer, the response bias generated from the generally low return rate of the mailed questionnaire survey has remained a problem. For over three decades researchers have generated a plethora of research on the effectiveness of the various aspects of the mailed questionnaire process and the resultant impact of various constructs on survey return . But despite these efforts, researchers have not succeeded collectively in producing a clear, compelling, or consistent set of principles that, if followed, will produce high response rates in mailed questionnaire research . With the certainty that more knowledge and constructs will be generated in all areas of the mailed questionnaire process, scholars have issued a call for a viable theory to direct future research efforts on response rates . Therefore, the purpose of this study was to address that need . The dissertation research reported in this paper accomplished five major objectives. It (a) developed an interdisciplinary theoretical framework for the mailed questionnaire process; (b) identified 13 determinants of response costs in the mailed questionnaire process; (c) proposed immediacy and salience as the most significant determinant variables of response rates, from a synthesis of the research literature with the theoretical framework; (d) proposed a theory and theoretical model that explain and illustrate the interaction of immediacy and salience in determining response rate levels; and (e) recommended a method for testing the proposed theory and for utilizing the proposed theory to achieve high response rates in future mailed questionnaire studies.