Due to several shifts in the construction industry, organisations start to collaborate. An example of this inter-organisational collaboration is a strategic alliance. Such an alliance can be defined as a close, long-term, mutually beneficial agreement between two or more partners in which resources, knowledge, and capabilities are shared with the objective of enhancing the competitive position of each partner (Spekman, Forbes, Isabella and MacAvoy, 1998). 50 to 60% of those alliances fails and one aspect for success is the organisation (De Man, 2006; Kalmback and Roussel, 1999). However, not much research has been performed to the organisation (Albers, Wohlgezoen and Zajac, 2013). This thesis focusses on the organisation of strategic alliances in which the Dutch engineering agency Sweco participates. Based on the grounded theory approach, the phenomenon strategic alliances has been explored. The combination of a literature review and an empirical research in which the cases Robuust Watersysteem, Ballast Nedam, Strukton and Dekker are analysed, has resulted in a first understanding of strategic alliances. The main conclusion is that strategic alliances in which Sweco participates are based on coincidence and do not have a very clear organisational structure. Hypotheses are that instead of strategic alliances, the collaborations are more tactical alliances. Second one is that there is a relation between the number of participants and the organisational structure. Final hypothesis is that due to the project-based orientation of the construction industry, strategic alliances in this industry are less likely to succeed compared to alliances in a less project-based orientation