Abstract of thesis entitled “The Path and the Castle. A Comparative Study of The Path of Purification of Buddhaghosa and The Interior Castle of Saint Teresa of Ávila: An Analytical Study on their Similarities in the Dynamics of Spiritual Life.” Submitted by Millet Gil, Daniel for the degree of Doctor of Philosophy at The University of Hong Kong in June 2019 Parallels between the spiritual paths of Theravāda Buddhists and Discalced Carmelites have long been observed, although not satisfactorily explained. This study contributes to objectively clarifying the similarities and differences between the two paths; and to explain their phenomenological similarities and structural affinities. This latter goal is carried out by identifying relationships between both religious systems and determining if there is an underlying level where they converge, irrespective of their undeniable differences. To achieve this end, the research comparatively examines the dynamics of spiritual development as described in two iconic works from the respective traditions: The Path of Purification (Visuddhimagga) by Bhadantācariya Buddhaghosa and The Interior Castle (Castillo interior) by Saint Teresa of Ávila. The thesis focuses on the stages of virtue (sīla) and concentration (samādhi) in The Path of Purification, and the Mansions One to Six in The Interior Castle where the similarities are more pronounced. After introducing the rationale that leads to the research and its expected outcome and delimitations, the study discusses some of the critical theoretical and methodological problems and issues that arise when engaging in interreligious and cross-cultural comparisons. It then reviews a series of methodological contributions by the school of New Comparativism, whose principles and tools are adopted throughout the study. The research goes on to introduce the background information requisite to understanding the doctrines of spiritual development as laid out by Buddhaghosa and Teresa. After presenting the comparands and their works, as well as their respective cultural and socio-historical contexts and influences, the study offers an overview of our two authors taxonomies of stages, and their notions of the nature and structure of the human being.