a long time “function” has become one of the key terms widely applied in architectural theory, design, critics, history and education.  Therefore it seems it has a clear meaning and simply can be used in different fields of architectural practice, design, education and theory. Thus function is considered as the most obvious concept in architecture and its very beginning point. But even a simple review of the concept and meaning of “architectural function” in history of architectural theory reveals many complications in the meaning and designations of “function”. The concept of function in architectural theory has begun in Roman era with the introduction of “utilitas” (utility) by Vitruvius and has since been continued and in some instances replaced by other terms, mainly “commodity” and “convenience”. The term “function” was introduced to architectural theory no sooner than 18^th century. In this article the author has attempted to review the terms and words indicating the concept of “architectural function” throughout the history of architectural theory along with other terms that have been used to describe them, i.e. “use”, “practicality”, “fitness for purpose” and “necessity”, in order to reach a terminological and etymological analysis of the concept. So the research can be considered as a basis for a clearer explanation of the architectural function as a fundamental term. The article has two main parts. In the first part, the related terms and words have been selected from the literature of architectural theory, and studied terminologically; i.e. in their corresponding context and etymologically, i.e. as general words. In the second part the interpretation of the terms in architectural theories are comparatively discussed. The results show that the meaning and application of these terms and words in architectural theory is related to four main interpretations of the concept of function; “Pragmatic”, “Organic”, “Mechanical” and “Systemic” interpretations. In “Pragmatic” interpretation, concept of function deals with the use of architecture in accordance with the human needs. “Organic” interpretation describes function as a natural interrelationship of all parts and the whole as an organism. In “mechanical” interpretation, concept of function deals with the interrelationship of all mechanical forces inside the architecture as a thing. Finally, the “systemic” interpretation describes function as the fitness for an end in architecture as a system. The multiplicity in number and origins of these four interpretations has played a main role in the complexity and ambiguity of the concept of function. Therefore, the meaning and concept of function is strongly related to the interpretations which are corresponded to the different and multiple theories of architecture. The study shows that the multiplicity of origins of the term “function” and its potentiality to correspond with different interpretations has been a strong reason for application of “function” as a general term. But the author has concluded that no clear explanation of the concept of architectural function is possible without a corresponding theory of architecture. So a single definition of architectural function is merely possible in the context of a single theory of architecture