The intention of the article is to present some of the linguistic and extra-linguistic aspects of the interpreting process, i.e. a process of the bilingual communication. Theoretical background of the issue is formed by interdisciplinary approach to the questions of sociolinguistics. Interpreting in one of its basic forms (i.e. consecutive) represents spoken communication and makes great cognitive demands on interpreters the essential part of which is made up by memory and concentration and another situational context. An interpreter is perceived as a bilingual individual characterized by proficiency in both language systems. The article also deals with language contact, i.e. bilingualism, code switching, language transfer, interference, etc., of two closely related languages – Polish and Czech.