This chapter discusses bilinguality from a socio-linguistic perspective. That is, how an individual bilingual interacts in societies with his or her languages and how a bilingual society and language varieties and dialects can be developed because of interactions between bilinguals. An individual bilingual's common practice of mixing different languages in their communications in societies, i.e., code-switching, code-mixing, and translanguaging is discussed. Then this chapter continues to discuss another bilingual practice commonly found in societies: translation and interpretation. That is, the time when bilinguals are required to maneuver between two languages in a limited time. The author suggests that translators or interpreters should take speakers' emotion, cognition, perspective, and the multimodal aspects of the environment into consideration in the process of translating or interpreting.