The focus of the monograph is on hierarchical systems of lexical items, particularly in scientific terminologies. It includes research outcomes from the dissertation Lexical Hierarchies in the Scientific Terminology, supplemented with a broad introduction to the typology of lexical and semantic relations and to a variety of branching and non-branching hierarchies, proportional series and other types of lexical configurations. It analyses the principles of formation of terminological classificatory hierarchies and identifies sense relations between items at superordinate and subordinate levels, and those at the same level. Specific morphological and onomatological properties of different languages influence consistency of corresponding lexical hierarchies, altghough the conceptual systems are identical.