Problem: Limited research exists regarding the professional development program processes and components used to train instructors to equip students with intellectual and developmental disabilities to receive greater support and access to the benefits of a postsecondary educational experience. Purpose of the Study: The principal purpose of this research was to conduct a multiple case study of inclusive postsecondary education (IPSE) programs known as Transition Programs for Students with Intellectual Disabilities (TPSID) and/or Comprehensive Transition Programs (CTP) at institutions of higher education across the United States to examine training provided to instructors teaching students with intellectual and developmental disabilities (IDD) who were enrolled in typical college courses. Method: A qualitative, multiple case study design was used. Five IPSE programs across the United States comprised the sample for this study. Two types of sampling were used: convenience sampling and non-probability or purposeful sampling. Convenience sampling was used to select the five IPSE programs based on their willingness to participate and provide the needed documents for analysis. Purposeful sampling was used to select the interview participants based on their ability to provide the most insight and understanding of the instructor training processes. To provide a comprehensive examination of the four research questions related to the training development, components, implementation, and evaluation processes for instructors teaching IPSE program students in typical college courses, interviews of the training affiliates, training observations, and document analysis were conducted within the five programs. Results: There is no unified approach to the training of instructors teaching students with IDD in IPSE programs. However, similarities exist in the training development, implementation, and evaluation processes used across programs. In conjunction with knowledge, skills, and practices, potential barriers to success such as the attitudes of instructors must be addressed. The roles of training affiliates in the development, implementation and evaluation of the training were described. Conclusions: The landscape of higher education is changing to provide access and inclusive learning opportunities to a more diverse group of students. There is hope that the institutions of higher education will begin to adopt the teaching and learning practices that best meet the needs of the new and growing group of learner types. Although there has been some progress, much work remains to be done to ensure that instructors are equipped to support the success of students with IDD and other diverse learners. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]