This volume brings together original papers from language education scholars from around the world to explore, exemplify, and discuss the multiplicity of boundary crossing in language education. It emphasizes the potential of boundary crossing for expansive learning, and aims to generate new insights, through boundary crossing, into the complexity of language education and approaches to innovative practices. This volume also underscores the important role of expert boundary crossers. In particular, it aims to honor G. Richard Tucker, Paul Mellon University Professor Emeritus of Applied Linguistics at Carnegie Mellon University, celebrating his distinguished scholarship on language education and paying tribute to the inspiration and mentorship he has given to the contributors of this volume to cross boundaries academically and professionally. This volume is organized into four sections, namely, language learning and development; teachers and instructional processes; program innovation, implementation, and evaluation; and language-in-education policy and planning. These sections or themes, which are necessarily cross-cutting, also represent the major areas of scholarship where Prof. Tucker has made distinguished contributions for over half a century.