Theoretical and methodological aspects of a theory of personalization are dealt with. The latter is centered around a specific aspect in the existence of an individual as a personality - his ideal representation and extension in the life activities of others. In this context the concept of "reflected subjectness" (one's existence in an other and for this other) is introduced and discussed in detail; the concept is further used as a framework for elaboration of the reflected subjectness method (analysis of an individual personality through its representation in the life activity of other people - in their motives, perception etc.). Concrete examples of experimental realization of the method are presented.