This Study investigates the syntax of complement and relative clauses in English which lack overt complementizers (clauses without that ). The central analytical claim is that these clauses differ in phrase structure from their synonymous counterparts with overt complementizers. In particular, novel evidence from adjunction facts is used to demonstrate that clauses without that are more appropriately analyzed as bare sentences of the category IP rather than CP with a phonologically null head, a proposal which has since been adopted in many economy-driven approaches to phrase structure. In addition to strong empirical support, the IP-analysis is shown to provide explanations for a variety of related syntactic phenomena, superior to those available under the previous CP-analysis. These include the restricted syntactic distribution of that -less complements, in addition to the adjacency restrictions on that -less relative clauses. The analytical task posed by the that -trace effect is also very much reduced under the IP-analysis. The work also examines the syntax of 'subject contact clauses' (e.g. There's a man wants to see you .), common in many non-standard varieties, including Hiberno-English and establishes that they have all the distinctive properties of other that -less relative clauses. This book will be of interest to a broad variety of readers: scholars working in all areas of generative syntax, specialists in English and Germanic syntax, in addition to researchers in non-standard English and Hiberno-English.