The basic focus of this book is to present the origin, the nature, the research methodology and the application of the concept Emotional intelligence. The presented study is a complex approach to EI synthesizing different kinds of theoretical models and research findings. The research is based on a multi-dimensional model of EI including cognitive and non-cognitive abilities, personal traits, performance variables, and social-demographic characteristics. The paper indicates the results from several methods measuring EQ (Schutte et al.'s questionnaire, Andre's questionnaire, Lioussine's questionnaire) and the results from several questionnaires measuring related constructs and components of emotional intelligence, such as empathy, need for achievements, optimism, occupational interests, stress, etc. The author hopes that the broad spectre of the used research methods and the various theoretical models of EI would make this book interesting and useful for a wide range of readers.