"In this volume, I discuss the topic of being able to speak two or more languages from three different orientations: bilingualism, bilinguality, and bilingual education. Bilingualism is more theory-oriented discussed at three levels: the individual level, the societal and institutional level, and the national and international level. Bilinguality, on the other hand, focuses more on the cognitive and neuro-linguistic parts of language function. That is, how bilinguals function in their brain while dealing with two or more languages. Finally, bilingual education presents the practical part of how language learning and acquisition is arranged in different areas of the globe based on their historical backgrounds and language policies. Detailed sub-topics will be introduced in the Introduction part"--