The book introduces the theory of words and vocabulary in the German language. Its subject is of such complex nature that the literature on it is hardly manageable, allowing for only the fundamental issues related to the lexicon to be addressed: the essence of the word as a basic linguistic unit, problems of word definition, concepts and types of motivation, word formation and meaning, the structure of the lexicon and the lexically-semantic relationships in text and system, the social organization of the German vocabulary, causes and driving forces of its changes, meaning shifts, the emergence of neologisms and archaisms, and the adoption of foreign vocabulary. The book is not a research monograph committed to any single one of the many current linguistic directions and schools, but aims to engage with as many studies as possible.