In a broad sense, PPP is a method of producing and delivering public services that brings together the public and private sectors in a long-term contractual relationship. Public and private sector resources are combined on the basis of a clearly defined division of tasks and risks. The purpose of this collaboration is to bring added value to infrastructure through innovation. PPPs are predicted on the assumption that in the private sector certain core competencies exist that can be drawn into infrastructure projects and that incentives can be written into the contractual arrangements to encourage the participants to find other parties who can bring extra value by way of complementary skills and synergies. PPPs are designed to maximize the use of private sector skills where these are needed to supplement the existing skills of the public sector, while ensuring clear accountability and risk transfer for both project delivery and operation. (Grimsey & Lewis 2004: 58 ; Greve & Ejersbo 2005: 257.)