Phenomenon of univerbation in communication of common and professional language users arises out of more reasons. Most of authors quote the tendency to language economy or elimination of contradiction between separated shape and united meaning of multi-word expressions (that are starting points of univerbation) as the most common reasons for existence of univerbation. This paper offers enumeration and short explanation of those and another reason for the phenomenon of univerbation, too. We perceive several tendencies as inter-lingual reasons for the univerbation. Language economy has hybrid inter-lingual-extra-lingual foundation and we differentiate three levels of it that depend on the type of univerbation. As extra-lingual reasons for the univerbation we consider a lot of pragmatic motives.