Over the past century, the Pentecostal and Charismatic movements have transformed the global Christian landscape with their emphasis on personal encounters with God. In this rigorous work, Andersen explains how Pentecostal experiences can also serve as a genuine source for Christian theology. Theology tends to draw upon traditional sources, those of Scripture, tradition and reason. Andersen brilliantly highlights how all these sources relate to the religious experiences, and how they all influence each other reciprocally in systematic theology. Through developing key criteria of how to evaluate these experiences, this book examines in detail what positive role Christian affections play in theological work and reflection processes. Highlighting the interplay between emotions and beliefs, the author combines Pentecostal theology of Christian affections with neuroscience and the somatic marker hypothesis. Finally, the book makes a cumulative case for the reliability of Pentecostal experiences of God. It synthesises arguments from the philosophy of religion to suggest a nuanced proposal of their distinct theological contribution as manifestation beliefs that represent relational and personal knowledge of God.