Purpose: The thesis has two objectives. First, from a theoretical perspective, it investigates the interrelationship between the theory of supply chain flexibility, the notion of leagility and the concept of 4PL. The second and primary objective is to explore the influence 4PLs have on leagile supply chain structures by integrating different types of both vendor and sourcing flexibility to analyse further whether 4PL providers facilitate a novel form of leagility. Design, Methodology & Approach: To suit the exploratory nature of the investigation, the thesis adopts an interpretivist, qualitative approach to research. Three semi-structured interviews were conducted with a sample of purposively selected 4PL providers. Furthermore, the study follows an abductive research approach because the underlying objective is not to test but rather to propose new theory in the field of supply chain management. The empirical findings are analysed based on a template analysis, while the quality of the research design is assessed by the criteria of credibility, transferability, dependability and conformability. Findings: From a theoretical perspective, a 4PL Leagility Framework is proposed that defines nine different types of leagility. These are generally interrelated; consequently, three particular categories were identified that determine the overall leagile configuration of a supply network: the family of sourcing leagility, vendor leagility or supplier leagility. Empirically, however, the framework could not have been tested to its full extent, meaning that none of the nine forms of leagility is validated. The study further concludes that 4PL providers may increase the level of flexibility within a supply network based on their expertise in coordinating and integrating the virtual supply chains and transportation networks. It is also argued that 4PL providers establish both sourcing leagility and leagile supply chain constructs, from the perspective of managing inter-organisational alliances. Limitations & Implications: The proposed framework may generally be applicable, although not without sacrifices. Practitioners would need to limit their service offerings to particular industry sectors and product categories. The framework neglects the coordination of 3PLs. Future research needs extend the sample of 4PLs to the fashion and beverage industry. Originality & Value: The thesis is a first attempt to integrate three different streams of research, namely, supply chain flexibility, the notion of leagility and the concept of 4PL. The thesis proposes a 4PL Leagility Framework that extends the leagility concept beyond the material flow decoupling point principle. Ultimately, the research illustrates potential approaches for 4PLs to facilitate leagile supply chain constructs.