What is mother tongue? Although the term mother tongue is very commonly used in general parlance, it has been variously defined with different connotations ever since its first appearance around 14th century in literature. A common dictionary definition of mother tongue would be: a parent language; one’s native language; the first language learned by a child and in which it can express fully and identifies with; the language learned by children and passed from one generation to the next, etc. In the translation industry, persons fluent in mother tongue or the native tongue are generally considered to have an edge over others for doing document translation to or from a language. It is generally understood when one refers to the term mother tongue that it is not only the language learnt from one’s mother but also is the dominant language, has mastered the linguistic and communicative aspects of the language. However if one grew up in some country where the local language is different from one’s home language, the native or the dominant language could be different from the mother tongue as defined above. Thus the common definition of the term mother tongue as given above is a little vague. Language experts have given more elaborate definitions of the term mother tongue. One of them defines the term depending on 4 different criteria: origin - the language(s) one learned first and established long-lasting verbal contacts, identification - the language(s) one identifies or is identified with (by others) as a native speaker of; function - the language(s) one uses most and competence - the language(s) one knows best.. By this definition, one can have more than one mother tongue. If one goes strictly by the definition of origin or identification, it is possible that one may know very little about his / her mother tongue but still would be identified with it as a native speaker. There can be more complicated situations in defining mother tongue when parents and children do not have the same mother tongue if one considers dominant language as the criteria. Also it is possible that the parents have different mother tongues and the language learnt in infancy may not be taught by primary care takers. Further in case of deaf children, sign language is the only language that they can express fully in irrespective of the language spoken by their parents. There are also cases of indigenous peoples wherein children may not have had the opportunity to learn their parent’s language or their ancestor’s language and in some cases there are no native speakers fluent in a particular native language. Thus a clear definition of mother tongue that is valid for all types of situations is elusive. Professional translation service providers however employ persons who have proven competence in the necessary languages whether it is their mother tongue or not. We will discuss issues like whether mother tongue offers any special benefit in achieving perfect translation in subsequent blogs.