Interplay management involves deliberate efforts by one or more actors to improve the interplay of institutions set up for earth system governance. This chapter synthesizes two decades of conceptual and empirical research on the conditions that influence the conduciveness of interplay management to earth system governance. Those conditions concern the agency and the means of management, notably whether interplay management proceeds by means of coordination or adaptation, as well as the compatibility of the policy objectives pursued. Agents of interplay management are states, intergovernmental organizations and industry- or civil-society groups, seeking to mobilize assets such as material resources, expertise or legitimacy held by one institution to promote objectives pursued under another. Means employed are frequently variants of unilateral adaptation to norms and programmes undertaken in other institutions, rather than explicit coordination involving joint decision-making. Cross-institutional coordination has obvious advantages and is particularly valuable when the institutions govern highly interdependent activities or can bring to bear complementary capacities. With clearly competitive elements present, adaptation has the advantage of triggering less turf-sensitive resistance.