These are difficult to describe accurately by means of a simple topology as many different types of contracts can be used (see Module 4). Apart from the usual distinctions in terms of the delegated services, ownership of the facilities or the point in time at which the operator intervenes during the lifetime of the project (operation and maintenance contracts, lease contracts, concession, BOT [build-operatetransfer], or BOO [build-own-operate] agreement, and so forth), particular attention will be paid to the problem of risk sharing between the port authority and the operator. All public-private partnerships are defined in a contract, the content of which must be adapted according to the characteristics of the particular project. These contracts reflect the mutual commitments of the parties and in defining them, the risks assumed by each party.