Historical entitlement theory tells us that no one, not even the state, may violate a person's property rights. A just society is one in which property is exchanged and distributed only voluntarily, and all socioeconomic relations are consensual and never coerced. Central to historical entitlement theory is self-ownership and its relationship to property in the external world. It is this relationship that this thesis explores. The thesis begins by developing and defending an alternative account of property in general. Under this praxeological account, property rights pertain not to physical objects as such, but only insofar as they are a means of action. Self-ownership, then, must be understood as a claim against interference in one's ongoing activities, so long as these activities themselves are non-interfering. A self-owner can therefore acquire rights to exclude others from natural resources insofar as those resources are subsumed into her ongoing activities. Where resources are exclusively subsumed, ownership is acquired, but where only non-rival use is made, a lesser bundle of property rights is acquired, which leaves space for the development of various kinds of commons. All property rights, however, are nothing more than rights to non-interference in certain uses of resources. The precise contours of these rights, then, are defined by the social conventions that determine the constitution of the particular activities within which resources are used. In revisiting the question of original appropriation I show that private property, where it can be justified, really does carry with it all the normative weight of self-ownership -- as Robert Nozick purportedly contended. However, other kinds of property systems are also compatible with, and even required by, self-ownership. Self-ownership not only protects our private real estate and chattel holdings, but also our rights to common resources. It is to the credit of self-ownership and historical entitlement theory that it is both compatible with, and provides strong deontic protection of, a variety of property systems, and does not assert -- as libertarians sometimes mistakenly do -- that private property is a panacea.