This thesis is concerned with establishing whether particular sourcing strategies lead to the achievement of sustainable competitive advantage, and the affect that the type of power relationships have on the situation. The theoretical framework for the study was grounded in the resource-based view. A survey was undertaken of twelve sourcing strategies within six organisations. The organisations varied in size and were from different industries. Furthermore, the sourcing strategies comprised six reactive and six proactive approaches and exhibited a varied mix of different power relationships. This enabled a thorough examination of the variables to be carried out. Three critical cases were then analysed in greater depth in order to investigate some of the contextual factors and second-order findings that were uncovered during the survey. The study found that proactive sourcing strategies may lead to sustainable competitive advantage, particularly when combined with buyer dominant or interdependent power relationships, but reactive approaches do not. However, a number of intervening variables were identified that also appear to influence the situation, such as the nature of the purchase, the objective of the sourcing strategy, and the degree of commitment to and investment in the sourcing strategy. A model is developed which explains the relationship between sourcing strategies and sustainable competitive advantage