Monograph describes the basic methods of computational linguistics applications for online marketing. The author accomplished the task of development of algorithmic support of processes of the content monitoring for solving the problem of defining the keywords of a Slavic language text based on Web Mining technology. Substantiation of peculiarities of its use for defining keywords and subject heading of the text content was considered. Web Mining technology allows us to take advantage of the text content monitoring method based on the Porter’s stemmer to solve the problem on determining the keywords. Stemming modification is based on the well-known classification of morpheme and word formation structure of derivatives of the Ukrainian language, revealing patterns of affixes combination, modeling the structural organization of verbs and suffixed nouns. Algorithms of morphonological modifications in the process of verb word changing and adjective word changing and word formation in the Ukrainian language were used. Decomposition of the method of determining keywords of the text content was performed. IAlgorithm support of its main structural components was developed.