Justin K. Stearns' 'Infectious Ideas' offers a profound examination of the metaphor of contagion within the sophisticated intellectual landscapes of Islamic and Christian thought. This compelling book explores how concepts of 'infection' and 'purity' were utilized to understand the spread and influence of beliefs, doctrines, and heresies throughout history. Stearns meticulously analyzes historical texts and theological discussions, revealing the intricate ways in which ideas, much like diseases, were imagined to transmit, transform, and impact societies. It’s an essential read for scholars of religious history, intellectual history, and the sociology of ideas, providing fresh perspectives on the dynamics of intellectual transmission across diverse cultural and theological frameworks.