The priesthood of all believers is a pillar undergirding Protestant ecclesiology. Yet the doctrine has often been used to serve diverse agendas. This book examines the doctrine's canonical, catholic, and contextual dimensions. It first identifies the priesthood of all believers as a canonical doctrine based upon the royal priesthood of Christ and closely related to the believer's eschatological temple-service and offering of spiritual sacrifices. It secondly describes its catholic development by examining three paradigmatic shifts, shifts especially associated with Christendom and a suppression of the doctrine's missional component. Finally, the book argues that a Christian doctrine of the priesthood of all believers should be developed with a Christocentric-Trinitarian understanding of the missio Dei. This suggests there are especially appropriate ways for the royal priesthood to relate to the Father, to the Son, and to the Holy Spirit. A canonically and catholically informed priesthood of all believers leads contextually to particular ecclesial practices. These seven practices are: Baptism as public ordination to the royal priesthood, Prayer, Lectio Divina, Ministry, Church Discipline, Proclamation, and the Lord's Supper as the renewal of the royal priesthood.