A recent survey carried out by Scottish Local Coastal Partnerships (LCPs) records sectoral interactions between coastal stakeholders using a colour-coded Sectoral Interactions Matrix (SIM). Stakeholders are encouraged to categorise their interactions with other sub-sectors, based on whether they felt conflicting, competitive, neutral or positive interactions were occurring. The term "managed competition", a phrase which emerged from the SIM work, is defined in this paper as an interaction where conflicting or competing coastal sectors co-operate to achieve a positive or neutral interaction which does not impact negatively on the wider coastal environment. Managed competition requires both targeted stakeholder communication, to allow resolution of inter-sectoral conflict, and scientific understanding, to find a balance that is also sustainable within the constraints of the natural carrying capacity of the environment. In successive SIM exercises, a reduction in the proportion of interactions categorised as competitive or conflicting with one another, matched by an increased percentage of positive or neutral interactions facilitated by managed competition, would represent a move to greater sustainability at the coast. Therefore, it is suggested that the SIM can be used as a measurement of sustainability at the coast, whilst managed competition can be used as a tool to achieve sustainability through resolving inter-sectoral conflict and ensuring that sectoral activities do not impact negatively on the wider coastal environment. Managed competition in practice is described using the illustrative case study of Montrose Bay at the northern extremity of the Tay Estuary Forum LCP region in east-central Scotland.