This dissertation answers the question what is and what is not ellipsis and specifies criteria for identification of elliptical sentences. It reports on an analysis of types of ellipsis from the point of view of semantic (semantico-syntactic) representation of sentences. It does not deal with conditions and causes of the constitution of elliptical positions in sentences (when and why is it possible to omit something in a sentence) but it focuses exclusively on the identification of elliptical positions (if there is something omitted and what) and on their semantic representation, specifically on their representation on the tectogrammatical level of the Prague Dependency Treebanks. In this dissertation, the dependency approach (used in the Prague Dependency Treebanks) is also compared with the generative approach (used in the Penn Treebank). It is possible to utilize this comparison in the (automatic) conversion from constituency trees to dependency trees.