This paper looks at specific type of private participation in infrastructure (PPI) projects called "unsolicited proposals." Unsolicited proposals are not requested by a government and usually originate within the private sector. These proposals typically come from companies with ties to a particular industry-such as developers, suppliers, and financiers-that spend their own money to develop basic project specifications, then directly approach governments to get the required official approvals. This paper focuses on unsolicited proposals that are natural monopolies or are in markets with limited or no competition (for example, water distribution concessions, toll roads, airports, and such). The premise of this paper is that some unsolicited proposals, when subject to competition and transparency, may contribute to the overall infrastructure goals of countries, particularly where governments have low technical and financial capacity to develop projects themselves. In particular, this paper looks at the processes of Chile, the Republic of Korea, the Philippines, South Africa and Taiwan (China) in detail.