While they often go hand-in-hand and the distinction between the two is frequently blurred, authority and power are distinct concepts and abilities - this was a problem that the Church tussled with throughout the High and Late Middle Ages. Claims of authority, efforts to have that authority recognized, and the struggle to transform it into more tangible forms of power were defining factors of the medieval Church’s existence. As the studies assembled here demonstrate, claims to authority by members of the Church were often in inverse proportion to their actual power - a problematic paradox which resulted from the uneven and uncertain acceptance of ecclesiastical authority by lay powers and, indeed, fellow members of the ecclesia. The chapters of this book reveal how clerical claims to authority and power were frequently debated, refined, opposed, and resisted in their expression and implementation. The clergy had to negotiate a complex landscape of overlapping and competing claims in pursuit of their rights. They waged these struggles in arenas that ranged from papal, royal, and imperial curiae, through monastic houses, law courts and parliaments, urban religious communities and devotional networks, to contact and conflict with the laity on the ground; the weapons deployed included art, manuscripts, dress, letters, petitions, treatises, legal claims, legates, and the physical arms of allied lay powers. In an effort to further our understanding of this central aspect of ecclesiastical history, this interdisciplinary volume, which effects a broad temporal, geographical, and thematic sweep, points the way to new avenues of research and new approaches to a traditional topic. It fuses historical methodologies with art history, gender studies, musicology, and material culture, and presents fresh insights into one of the most significant institutions of the medieval world.