We are often uncertain about the identity of objects. This phenomenon appears in theories of object persistence in early childhood; in the well-known Morning Star/Evening Star example; in tracking and data association systems for radar; in security systems based on personal identification; in the content analysis of web pages; and in many aspects of our everyday lives. The talk will describe a formal probabilistic approach to reasoning about identity under uncertainty in the framework of first-order logics of probability, with application to wide-area freeway traffic monitoring and citation matching.