This paper attempts to develop concepts of project and contract organization to pedict the selection of contract type on infrastructure projects. Conventional wisdom is that at low-risk fixed price contracts are best, moving to remeasurement and then cost plus as risk increases. We started trying to predict this from a transaction cost perspective, and such an analysis confirmed conventional wisdom. However, it does not fit with current practice. Further, the diffecences in transaction costs are small compared to differences in contract out-turn cost that occur under the different motivational efects of different cotract types. We therefore take a different perspective. We assume the purpose behind a project contract is to creat a coperative project organization, in which all participants, clients and contractors, are motivated to achieve commom objectives, their goals are aligned. This analysis confirms modern practice, and shows selection of contract type is related of uncertainty in the project`s deliverables, and uncertainty in the process of their delivery. Build-only remeasurement contracts are used where uncertainty of both product and process is low. Design and build fixed price contracts are used where uncertainty of the product is low, but the uncertainty in the process of delivery is high. Fixed price contracts should be used where both are high. We extend the analysis to show when the client should be involved in the project organization in an alliance contract, and when they should not, as in a traditional project contract