Res nullius (lit: nobody's thing) is a Latin term derived from Roman law whereby res (objects in the legal sense, anything that can be owned, even slaves, but not subjects in law such as citizens) are not yet the object of rights of any specific subject. Such items are considered ownerless property and are usually free to be owned.
Examples of res nullius in the socio-economic sphere are wild animals or abandoned property. Finding can also be a means of occupation (i.e. vesting ownership), since a thing completely lost or abandoned is res nullius, and therefore belonged to the first taker. Specific legislation may be made, e.g. for beachcombing.
In English common law, for example, forest laws and game laws have specified which animals are res nullius and when they become someone's property. Wild animals are regarded as res nullius, and as not being the subject of private property until reduced into possession by being killed or captured. A bird in the hand is owned; a bird in the bush is not. Even bees do not become property until hived.
Res nullius also has an application in public international law, more specifically called terra nullius, whereby a nation may assert control of an unclaimed territory and gain control when one of its citizens (often an exploratory and/or military expedition) enters the territory.
This terra nullius principle justified colonisation of much of the world, as exemplified in the "carving up" of Africa by the European powers (see Scramble for Africa). It is the concept that even though there may be indigenous peoples residing in "newly discovered" land, it is the right of the "more civilised" to take the land and put it to "good use".