Although first possession is generally assumed to be the dominant means of establishing original ownership of property, there is a second but less studied principle for initiating ownership, called accession, which awards new resources to the owner of existing property most prominently connected to the new resource. Accession applies across a wide variety of areas, from determining rights to baby animals and growing crops to determining ownership of derivative rights under intellectual property

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... laws. Accession shares common features with first possession, in that both principles assign ownership uniquely in a way that imposes minimal information cost burdens on society. But accession differs from first possession in that it does not presuppose that rights are established in an open access commons and does not require the performance of an act to establish ownership. These features of accession make it, as a rule, more efficient than first possession, at least where property rights are thick and securely enforced. More broadly, accession can be seen as the critical legal principle that generates the internalization function of property, insofar as gains and losses attributable to the management of resources are automatically assigned to the most prominently connected property by accession. Although the story of accession is generally a positive one from an efficiency perspective, it may be more problematic from several normative perspectives, which are briefly considered.