Leadership development is a widespread and burgeoning global enterprise, as well as a rapidly growing field of academic study. An estimated $50 billion is spent on leadership programmes annually (Kellerman, 2012) and yet, there is a large degree of confusion regarding what is known regarding optimal approaches, especially those that are tied to organisational outcomes. There is further confusion in terms of the evidence to reinforce such claims, as well as effective forms of measuring leadership, particularly after interventions. The aim of this dissertation is to address those two topics, as well as to assess the current state of literature in terms of leadership development for professionals. A novel methodology was employed called a systematic evidence analysis (SEA), which isolates multiple data sets and involves several stages and layers of analysis. This study involved three separate, but related literature reviews to generate these data sets. The first was a systematic review of leadership development for professionals in multiple domains that identified 56 studies. The second was a review of existing literature reviews on leadership development for physicians that included one non-systematic and six systematic reviews. The third was a systematic review of leadership development for physicians that included 25 studies. A validated instrument, the Medical Education Research Study Quality Instrument (MERSQI), was applied to each of the 25 aforementioned studies to critique their quality. Categories of evidence groupings were then devised based on commonalities among the included studies’ designs. The categories of evidence are: strong, good, moderate, limited, and anecdotal. Further stages of analysis involved investigating two of the conclusions from the best available studies in detail, as well as developing a prototype theoretical model of leadership development and evaluation. The results are that the overall quality of literature is quite low. None of the 25 studies qualifies as strong evidence, two are good evidence calibre, four are moderate, and the remaining 19 are either of either limited or anecdotal quality. The overall mean was in the anecdotal calibre range. Likewise, there were common flaws in the seven literature reviews that were analysed, including failing to tier the findings and conclusions according to the quality of evidence. Conclusions from the strong and moderate evidence studies include that workshops followed by videotaped simulations with expert feedback can improve observable leadership behaviour and contribute to self-awareness. Action-learning is effective in enabling participants to achieve organisational and benefit to patients/clients outcomes, among others. Leadership development has been found to lead to a variety of individual outcomes, such as increased confidence, self-efficacy, and career advancement. Further analysis revealed that Knowles’s (1984) principles of adult education is perhaps the most common educational theory applied to leadership development design. This thesis adapted and expanded his theory by adding two principles, as well as providing examples from the included studies. A second finding was explored in detail, which is the collection of factors before, during, and after interventions that facilitate or inhibit the application of leadership following programmes. These are important not only to enhance the impact of programmes, but to avoid common pitfalls that led several programmes to fail. The beginnings of a theoretical model are offered concerning the cardinal and complementary functions of different developmental activities, which can maximise their utility, especially in reference to specific programme objectives. Another product of the systematic evidence analysis is an outcomes-based prototype theoretical model of leadership design and evaluation. Finally, elements of quality research design and evaluation are presented, as is an overarching proposal to ameliorate the thin nature of the evidence in the field. The conclusions suggest that the state of the literature in the field needs to be improved. This can be done through a combination of stronger individual study and literature review research designs, better reporting, and tiered findings and conclusions based on the quality of the evidence. Outstanding specific gaps in, or extensions of, the knowledge base are included. This thesis provides a clear and transparent elucidation of what is known in terms of optimal leadership development for professionals and the evidence to reinforce it, which can potentially inform practitioners and serve as the foundation for further research. Similarly, those designing and delivering programmes can potentially use aspects of the two conclusions explored, as well as the two theoretical models, to guide their interventions. The intention is that doing so could increase the impact of programmes, as demonstrated by improved outcomes.