This study used a two-phased explanatory mixed-methods design to explore in-depth what factors are perceived by Instructional Design and Technology (IDT) professionals as impacting instructional design practice, how these factors are valued in the field, and what differences in perspectives exist between IDT managers and non-managers. For phase 1 of the study, one hundred and sixteen corporate IDT professionals (managers and non-managers) responded to a web-based survey that was designed and developed from: (a) The results of an exploratory study of the practices of corporate instructional designers, (b) the results of an extensive literature review into the theory and practice in the field of IDT, and (c) other survey instruments developed, validated and used in prior studies. Analysis of the data collected in phase 1 of the study resulted in the development of an Evaluation Model for IDT Practice that was used as a framework to answer the research questions. Quantitative analysis included the use of Hotelling's T2 inferential statistic to test for mean differences between managers and non-managers perceptions of formal and informally trained groups of IDT personnel. Chi squared analysis test of independence, and correlation analysis was used to determine the nature and extent of the relationship between the type of training and the professional status of the participants. For phase 2 of the study, semi-structured interviews were conducted with selected participants and analyzed using the constant comparative method in order to help validate the findings from phase 1. Ensuing analysis of the survey data determined that, both managers and non-managers generally agreed that both formal and on the job training was valuable, and that their peers who were formally and informally trained were competent instructional designers. The qualitative phase of the study and a closer examination of effect sizes suggested the potential for some variation in perceptions. In addition, a statistically significant correlation showed that IDT managers who completed the survey were more likely to be formally trained. Recommendations based on the results included future studies with a larger, more diverse population; future studies to refine the Evaluation Model for ID practice; and that academic ID programs work more closely with practitioners when designing and delivering their curricula. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]