This article analyzes the key concept of Samuel Taylor Coleridge's masterpiece Biographia Literaria: Imagination. It starts by untangling the personal background and the intellectual history of Coleridge's Imagination; secondly, discloses its great influence on literary writing, namely, Fantasy literature today; and lastly, introduces its use and impact in literary creation and criticism. The article aims to clarify the Christian dimension in British Romanticism represented by Coleridge, and re-evaluate the potential power of Romantic aesthetics.