This thesis focuses on the description of changes in the lexical and morphoderivational system of Standard Croatian language which come about as a consequence of lexical-semantic innovations and most frequently arise from social needs for naming new terms and concepts. The term neologisation encompasses all the processes guiding the formation of new words in the lexicon, which implies a very wide understanding of the term. The latter encompasses both newly-coined domestic words resulting from lexical creativity, and loan words, with special emphasis on Anglo-neologisms described on the basis of Filipović's (1986) theory of Languages in contact, as well as semantic neologisms enabling the language to keep its independence on the formal plane and is itself semantically enriched (e.g. mouse, virus, window). All the above categories are analyzed in the framework of denominative and connotative neology, i.e. based on whether they appeared in language to name new things that crop up daily from foreign and domestic sources, or result from the fascination with the foreign lifestyle (i.e. from linguistic snobism). Furthermore, we note a somewhat paradoxical position of neologisms between linguistic openness, i.e. the readiness to embrace new words which are "imported" along with new concepts, and purism, i.e. the initiative to coin new words by using domestic linguistic components, is closely related to connotative neology. It is thus indispensable in the analysis of neologisms to appraise fresh/ new attitudes on what is desirable or undesirable in language. With respect to the possibility of lexicalization, the thesis also looks into occasionalisms or hapax. Although the research on neologisms broaches on several important areas, the thesis primarily focuses on the level of word formation. Consequently, it examines the degree of productivity of domestic word formation patterns with respect to the influx of new word formation patterns, non-typical of Croatian. The thesis, furthermore, examines the sociolinguistic background of neologisation, describes the stand of the linguistic norm and purism toward neologisms, and establishes more elaborate criteria in their identification, i.e. filtering of the vocabulary referred to as neologisms. The thesis features a list of new and revived lexemes and word formation units as well as rules and ways of forming neologisms. New meanings, along with the extensions and narrowing of existing ones are listed. The thesis also examines changes in connotation, usage, frequency and productivity of individual lexemes and word formation units. The corpus of neologisms is collected by analysing different editions of the same dictionary and by comparing monolingual and bilingual dictionaries by different authors, with the first edition of Rječnik hrvatskoga jezika (Dictionary of the Croatian Language) by Anić (1991) serving as the starting point. The structuralist (Babić 2002) and the generative (Selkirk 1982) method is used for the description of word formation processes and rules, whereas the methodological apparatus of Cognitive Linguistics (Lakoff, Johnson 1980; Lakoff 1987) is used in the analysis of semantic neology. The first chapters introduce the basis theoretical approaches to the study of neologism, and basic processes governing neologisation. The central part of the paper is an analysis of the corpus of neologisms on the word formation level with special emphasis on determining changes in the Croatian word formation system, including those in semantics, frequency and usage of some lexemes. The final part is a synthesis of the research and places it within the broader theoretical framework of research on neologisms. The appendix features a list of recorded neologisms.