Purpose: The paper aims to discuss the emergence of communities of practice in a temporary event organisation involving public and private partners. Design/methodology/approach: The study employs qualitative methods in the form of 31 semi-structured interviews, a five-week period of participant observations and archive research in a Swedish public-private partnership, focused on large-scale media and entertainment event. Findings: In the temporary event-driven project-based organisational structure studied, communities of practice emerged by themselves because of the complexity of the task at hand. These are called "emergent communities of practice". Four built-in organisational mechanisms that cultivated the emergent communities of practice were identified: trust building stability; competence contributors; competence shadows; and social glue of informal events. Surprisingly, the public/private dimension was found not to affect the emergence of the community negatively. Research limitations/implications: Given that conclusions are based on the Swedish data, the paper recommends that similar studies be carried out in other countries. Originality/value: The paper extends the framework of communities of practice beyond the boundaries of a single or few stable organisations by analysing communities of practice within a temporary project organisation; it introduces the concept emergent communities of practice; and it proposes four ways to cultivate communities of practice.