This book presents a unified formal approach to various contemporary linguistic formalisms such as Government & Binding, Minimalism or Tree Adjoining Grammar. Through a careful introduction of mathematical techniques from logic, automata theory and universal algebra, the book aims at graduate students and researchers who want to learn more about tightly constrained logical approaches to natural language syntax. Therefore it features a complete and well illustrated introduction to the connection between declarative approaches formalized in monadic second-order logic (MSO) and generative ones formalized in various forms of automata as well as of tree grammars. Since MSO logic (on trees) yields only context-free languages, and at least the last two of the formalisms mentioned above clearly belong to the class of mildly context-sensitive formalisms, it becomes necessary to deal with the problem of the descriptive complexity of the formalisms involved in another way. The proposed genuinely new two-step approach overcomes this limitation of MSO logic while still retaining the desired tightly controlled formal properties.