Based on one of the richest surviving diaries of the Dutch Golden Age, *Princely Power in the Dutch Republic* recaptures the social world of William Frederick of Nassau (1613-1664). As a Stadholder and relative of the Prince of Orange, William Frederick was among the key players in a fragmented republican state system. This study offers a vivid analysis of his political strategies and reveals how unwritten codes of patronage guided his daily contacts and shaped his mental world. As a patron at his court and as a client of the Prince of Orange, William Frederick developed distinctive patronage roles, appropriate to different social spheres. By assessing these different roles, Janssen provides a unique insight into the ways in which a seventeenth-century nobleman negotiated and articulated clientage, friendship and corruption in his life. This study offers an in-depth analysis of political practices in the Dutch Republic and reconsiders the way in which patronage shaped early modern politics, affected religious divisions and framed social identities.