The aim of this study is to provide theoretical rationale for integrative model of motivation as a unified structure that ensures achieving different types of results of human activity. The methodology of this study includes induction and deduction methods, scientific literature analysis, as well as comparative analysis. There have been defined the notions of «motive», «need» and «motivation», in particular, we have identified major differences and similarities between these concepts as well as their points of contact. The motives have been classified into conscious and unconscious with subsequent justification of such division. The article discusses the difference between external and internal motivation and proves the particular effectiveness of the latter. There has been analyzed the structure of the human motivational system encompassing all its components such as interests, needs, values, attitudes, beliefs, stereotypes, etc. We have identified the basis of motivational system, which determines personality's orientation and its peripheral parts. There has been conducted a comparative analysis of major motivation theories, which explain the structure and significance of human needs, their relationship with motivation to act. For example, we found out that K. Alderfer's ERG paradigm corresponds to A. Maslow's hierarchy of needs paradigm in regards to the main groups of needs. However, most theories of motivation use different criteria for distinguishing needs which makes it more difficult to compare them. For instance, D. McClelland's acquired needs paradigm is based on identifying the needs for power and complicity, while Porter-Lauler model is based on analysing concepts of expectations and justice within the motivational system of an individual. However, all authors seem to agree on one thing: motivation is a complex system-based integrative psychostructure that encourages a person to perform various types of activities. Thus, we can conclude that despite various explanations of the concepts of «motive» and «motivation», different criteria for distinguishing needs and interpreting their impact on motivation, human motivational system is a holistic unified structure that affects human behaviour in a specific way.