This chapter discusses the concept of Sign-Based Construction Grammar (SBCG), which evolved out of ideas from Berkeley Construction Grammar and construction-based Head-Driven Phrase-Structure Grammar (HPSG). The leading insight of SBCG is that the lexicon provides a model for the syntax-semantics interface. The chapter explains that though SBCG cannot be divorced from the formal conventions it uses to represent lexemes, constructions, and the hierarchical relations among types, it offers insights to construction grammarians whose work is not primarily formal. It also considers the strict locality constraint of SBCG, the avoidance of overgeneralization, inheritance, as well as the treatment of inflectional and derivation processes.