This chapter analyses progressive property theory in more detail, assessing the membership of that school of thought, the range of perspectives on the mediation of property rights and social justice that it captures, and its core themes and traits. It also addresses the property values that are captured in progressive property's pluralistic approach. These include efficiency, autonomy, and personhood. In doing so, the chapter signposts ideas about the relationship between property rights and social justice that influence Irish constitutional property law, in order to assist the reader in understanding the immanent, evolving, and often partial influence of property theory in the doctrine and outcomes of Irish constitutional property doctrine that are analysed in subsequent chapters. These values can help to explain the intuitive approach that is identifiable in much judicial reasoning in constitutional property law.