The definition of optimal shape and scope of blended learning trainings was one of the main aims of the presented article. The authoress was trying to find out 'what is the most optimal and efficient didactical process of the blended learning training concerned as a systemic element of reality'. As a result of holistic research, it was possible to distinguish some fundamental components of e-learning process (both in its fully online as well as in blended form) that guarantee its optimization i.e. identification how to ensure its efficiency and sustainability. There is also a presentation of the author's didactic model of blended learning trainings realization (including connection, correlations and sequence of online and traditional parts of training). This model was prepared as a result of research regarding the system theory approach to blended learning trainings.