Research in the Quantum Information Sciences has exploded since the 1980s, with fascinating results across new fields such as Quantum Cryptography, Quantum Computing and Quantum Information Theory. However, the deep connections between Quantum Measurement, Inductive Logic and the theory of Bayesian Inference have been comparatively less developed. In this work, a facsimile reprint of a 1989 University of Bristol PhD thesis, the reader encounters the formative stages of the theory of Quantum Bayesian Inference. Sections of this thesis were later published [KRW Jones: Annals of Physics, 207 140 (1991)], but the full text contains many previously unpublished computational tricks and asides that will likely be of interest to current workers in the field. It may also prove useful to those who study the historical process of how novel scientific ideas emerge, develop and cross-fertilize across diverse global research centers.