A study identified adult learning principles critical for effective Web-based instructional design (WBID), barriers to effective WBID, and practices of professionals who design WBID. National experts in adult education and WBID were interviewed, and the resulting product was an online assessment that 10 Web-based instructional designers completed. Electronic document analysis of Web-based training/instruction was completed to examine the actual practices of instructional designers. Findings indicated the following: (1) 36 principles were found critical for design of effective Web-based training or instruction; and (2) 3 barriers that impede successful implementation of Web-based training or instruction were instructor accessibility and responsiveness, instructor's expectation of students, and fostering a participatory online learning environment. Asked to identify which of a subset of 22 adult learning principles they applied in design of Web-based courses, 100 percent of instructional designers said they applied 7 principles and 80 percent applied 3. Their courses were designed to allow learners to share experiences; to include aids that help relate new material to current knowledge and prior experiences; to provide graphics, examples, cases, analogies, and activities; to include checkpoints; and to allow learners to be self-directed. The researchers believed this project has implications for instructional design, professional development, and student retention. (Contains 25 references.) (YLB)