The wealthy Katerina Lemmel entered the Maria Mai monastery in 1516--and rebuilt it. In Katerina's Windows, readers can observe how stained glass was donated and commissioned and witness spectators' reaction to it, ranging from critical aesthetic assessments to iconoclastic acts. The book presents historical texts and interpretive analysis. Katerina Lemmel and those around her are given voice through translations of seventy-three sources, including personal and business letters, chronicle accounts, and legal documents, most of which have never been transcribed or published before. Necessary explanations as well as theoretical considerations and critical insights are provided through the voices of the authors. Katerina Lemmel's letters allow glimpses into the materiality of monastic life; views of the interconnected workings of art, music, liturgy, and literature; evidence of the persuasive powers of a nun who functioned as negotiator; accounts of one woman's struggles on behalf of other women; and data on women's networks. The sources provide insiders' insights into the spiritual economies later scorned by Protestant reformers. They also offer an eyewitness account of the social challenges to this system that erupted in violent clashes during the Revolution of 1525. The material offers a fresh look at art and music made by and for nuns. Much previous literature has focused on nuns as mystics and visionaries, and on their art as primitive or mundane. This book demonstrates the roles of nuns as active agents for sophisticated art and innovative liturgical music.