This book offers a long-awaited unified and precise treatise on construction-based grammar. The approach to grammar presented here is the union of Berkeley Construction Grammar, as represented by the early work of Charles J. Fillmore and Paul Kay, with construction HPSG as pioneered by Ivan Sag, Carl Pollard, and others. The presentation of this theory in a detailed chapter by Sag presents the full outlines of a new approach to grammar. It reflects the confluence of two separate, although converging, traditions, and constitutes a novel synthesis.