This accessible volume presents an up-to-date overview of how young children, older youth, and adults develop multilingual proficiencies. Importantly, it highlights an assets view of multilingualism, offering clear recognition that multilingual competencies are both functional and highly valued in communities across the globe. Dispelling common myths, it explores the benefits of multilingualism spanning interpersonal, academic, and professional settings. With these settings in mind, the book provides practical information on how professionals can promote effective communication with colleagues and clients from a variety of language backgrounds. Each chapter comes equipped with a series of true or false statements where you can record your predictions and learn as you read. Chapters cover topics including the economic and cognitive benefits of multilingualism, social influences, the age factor, family bilingualism and optimal teaching and learning conditions. Finally, the book concludes by providing various step-by-step resources for creating optimal conditions that further develop and support multilingualism in your professional field. Containing suggestions for research-based practices in home, school, and professional settings to enhance multilingual development, this book is essential for professionals working with multilingual young children, older youth, and adults, as well as those who require a foundational understanding of multilingualism.