The book is about research of the sentiment analysis of the natural language text. In particular, text tonality indicators are considered. Approaches to sentiment analysis are also analyzed. The description of the existing systems of definition of a tonality of the text is described. The program system of the automated sentiment analysis of the text is developed. The description of methods and algorithms of text processing is provided. The used tools and structure of the processed data are considered. Experiments according to the analysis of operability of the realized algorithm of the sentiment analysis of the text are made.