This document summarizes Systemic Functional Linguistics (SFL), an approach to language developed by M.K.A Halliday in the 1960s. SFL considers language as a social semiotic system based on five principles: social semiotics, language as a resource, text rather than sentences, text and social context, and construing meaning. It discusses how SFL analyzes language through three metafunctions - ideational meaning, interpersonal meaning, and textual meaning. The document also describes how SFL is used in genre-based grammar to teach students to effectively use writing codes like genre and grammar.