This book presents a comprehensive study on the phenomenon of projection in English language, drawing upon Halliday's systemic functional linguistics (SFL) model. It aims to clarify the grammatical status of projecting and projected clauses and explore their synchronic distribution features as well as diachronic evolution patterns. This book provides insights into the understanding of the grammatical status of projection-related clauses. Furthermore, the uncovering of historical evolution trends contributes to the literature on grammatical metaphor in SFL. From a practical standpoint, the empirical investigations into the relationship between projection and text technicality provide important implications for English teaching pedagogy and discourse analysis.