This book is a collection of essays, some previously published and some recent papers appearing in print for the first time, that have a number of things in common. First, they are nontechnical papers that I hope can be read by nonspecialists. Second, they all assume the correctness of my theoretical work in language acquisition, but make no attempt to defend it or even to review the many studies it is based on. This is done elsewhere. The essays in this volume explore some extensions and applications of the theory and illustrate how the theory helps provide insights and solve problems in several areas.