Old Catholic theology is the theology that is characteristic of the Old Catholic Churches of the Union of Utrecht. Old Catholic Theology: An Introduction, authored by Peter-Ben Smit, an acknowledged expert in the field, outlines the main characteristics of and influences on Old Catholic theology, as well as the extant ecumenical relationships of the Old Catholic Churches. In doing so, it covers what may be called ‘mainstream’ Old Catholic theology, while also discussing the diversity within the Old Catholic tradition. Particular attention is given to the Old Catholic approach to theology in general and to ecclesiology, sacramental theology and ecumenical theology in particular. Further foci include the version of communio-theology, the appertaining sacramental understanding of the church, the inherent connection between theology and (liturgical) spirituality, the distinct branch of communal hermeneutics and the understanding of the appeal to the early Church that Old Catholic theologians developed in the course of the 20th century.