The discussion in this chapter is divided into four parts, apart from the introduction and conclusion. In the first part, a brief explanation of the term ‘multilingualism' is made and the phenomenon is described with references to its occurrence in the world, Africa, Nigeria and individuals. The second part discusses language and national development by examining the indices of national development of which language is an integral part. The third part describes language planning and language policy by focusing on the types and activities of planning as well as policy decisions and provisions on language in Africa/Nigeria. Lastly, the implications of language policy and planning for national development are observed by identifying the desirable goals of the Nigerian nation and then suggesting some steps for removing the constraints on language planning and policy formulation. In all, while the study has only attempted to study salient issues in the field, it does not claim to have fully exhausted the points or treated all the issues in detail. Students will nonetheless find the paper to be a useful introduction on the subject area.