Catalonian Affairs examines the actions of the French army in Catalonia (1635-1659) using previously unused French and Catalan archival sources. It provides detailed descriptions of the units involved from both the French and Catalan allies for each campaign. Catalonian Affairs also explores the beginnings of uniformity, the tactics, and the weaponry used in the region. Additionally, it covers the naval aspect of the conflict and discusses how the armies were financed. This first volume covers the events from the start of the conflict in 1635 up to the Fronde crisis in 1648. It uses first-hand accounts to shed light on the lives and actions of those involved. A second volume will describe the fall of French Catalonia and the campaigns to recover it, the naval battles of Barcelona in 1642 and Cabo de Gata in 1643, and the Lérida battle in 1642, the largest battle of the conflict.