We formulate and discuss a general axiomatic theory of arbitrary objects. This theory is expressed in a simple first-order language without modal operators, and it is governed by classical logic. The theory AOT intends to be a fundamental and a fully general (and somewhat flexible) theory of arbitrary objects. Ideally, it intends to be a suitable formal framework for all legitimate applications of arbitrary object theory. According to the proposed theory, arbitrary objects are organised in correlated systems, where each such system of arbitrary objects is abstracted from a system of particular objects.