State, regional, and municipal authorities, public transport authorities, and traffic operators at many levels are essential actors in public transport. This paper presents a typology of four coordination mechanisms relevant to interactions among public transport actors. These four mechanisms, i.e. ownership/instruction, contracts, partnerships, and mutual understanding, are all based on basic coordination mechanisms of markets, hierarchies, and networks. A case of timetable planning is examined, because inter-organisational coordination between actors is crucial in this field, and the usefulness of the typology is illustrated via three examples. The results stem from a Danish study of institutional constraints on timetable optimisation in inter-organisational relations. The empirical focus is eastern Denmark, including Greater Copenhagen.