Abstract: This paper discusses trust and trust perceptions in infrastructure contracts and supporting institutions. We focus on perceptions of the trustworthiness of the government purchasers of infrastructure services by the supplying companies and by the governments themselves. In particular, we allow for trust updating and trust misalignments which may give rise to ‘undertrusting’ and ‘overtrusting’. The core of the paper sets out a game theoretic model of contracts with dynamic adjustment of trust perceptions, which we use to explore the impact of trust misalignment both on economic efficiency (measured by economic welfare) and on investment levels. We explore flexible contracts with and without pre-payments, rigid contracts (which do not allow for post-investment renegotiation) and hybrid contracts. We then compare the efficiency of the flexible contracts to that of the hybrid contracts using as a criterion the expected welfare implications of each contract. The model is used to shed light on current issues on the sustainability of private investment infrastructure contracts in developed and developing countries, including the role of regulatory institutions.