Frame Semantics is foundational to Construction Grammar in both chronological and conceptual terms. Originally developed by Charles J. Fillmore in the late 1970s to 1980s as a theory of semantics that prioritizes language users’ human experience, it views the meaning of linguistic elements in terms of a network of empirical information, which, in turn, motivates the concept represented by the linguistic elements. The theory laid a rich foundation for a variety of approaches associated with Construction Grammar and remains an intellectual resource for further research developments. This chapter focuses on the seminal ideas of Frame Semantics, further advanced in relation to Construction Grammar and the FrameNet project. After an overview of the theory, a variety of frame concepts (e.g., cognitive frame, interactional frame, and linguistic frame) are discussed. We then turn to how frames can effectively explain grammatical ‘well-formedness’ as illustrated by two case studies that were conducted on the path from Frame Semantics to the establishment of Construction Grammar. The last section discusses implications and prospects for the theory of Frame Semantics.