The research described in this thesis is aimed to improve our knowledge of barriers to the use of OR (Operations Research) techniques in the manufacturing sector. Numerous issues have been previously identified, but the work has generally been unsystematic, or focused on the OR profession. This research is empirical, systematic, and compares a group of OR professionals to a group of manufacturing managers. The technology selected for analysis was DES (Discrete event simulation, a computer based technique for modeling complex manufacturing processes), and the companies chosen, as the focus for data collection, were based in Australia. Two major implications for practice are identified in the thesis. These two perspectives should be seen to be complementary, rather than opposing. OR professionals should place their knowledge within the mindset used by manufacturing managers, rather than attempting to displace that mindset. / Doctor of Philosophy (PhD)