This is an Element about wonder as an object, as a feeling, as an invitation to study, and as a way of thinking in both literary and scientific texts of the long eighteenth century. Wonder is at the heart of natural philosophical inquiry in the long eighteenth century, its inaugural provocation, its long-standing problematic. Yet wonder requires observation and imagination, operating together, if uneasily, to give shape to forms of scientific, literary, and social knowledge, shaping how thinking works and who can do it. Studying wonder in the long eighteenth century helps us to understand our current disciplinary configurations, and also how wonder itself embodies the potential for a more capacious critical practice. Studying wonder as an epistemology, praxis, and thematic in the long eighteenth century also carries the promise of invigorating and reimagining our own critical, creative endeavors.