Kyle J. Dieleman focuses on the doctrinal and practical importance of Sunday observance in the early modern Reformed communities in the Low Countries. My project investigates the theological import of the Sabbath and its practical applications. The first step is to focus on how Dutch Reformed theologians conceived of the Sabbath. The theology of the Sabbath, I argue, moves over time from an emphasis on spiritual rest to participating in the ministries of the church to a strict rest from all work and recreation. The next step is to explore congregants' actual Sunday practices. By attending to church governance records at the national, regional, and local levels the importance of proper Sabbath observance quickly becomes clear. The provincial synod records, classes' records, and consistory records indicate that church authorities were adamant that church members faithfully attend sermon and catechism services, refrain from sinful practices, and abstain from recreational activities. Equally as telling as the observance demanded of church members is how church authorities responded. The church records portray these authorities as fretting over the disordered and unregulated nature of improper Sabbath observance. Having established the importance of the Sabbath in Dutch Reformed theology and lived piety, I argue the emphasis on Sunday observance is best understood as resulting from two main factors. First, the emphasis on proper Sunday observance is a result of the Reformed church authorities attempting to maintain the pious reputation of the Reformed faith and establish the identity of the Reformed Church amid multiple other confessional identities. Second, proper observance of the Sabbath was important because it ensured order within the church and society more broadly.