This paper is based on the grounded theory study, in which experienced music therapy clinicians were interviewed and their conception of an initial assessment were examined in detail. The main result of the study is a qualitative synthesis of initial assessment procedures, including the description of the process how a therapist gains his/her understanding of a client during an assessment period. In practice, an overall structure and a setting of assessment sessions enable practical activities, which are client-centered and usually non-structured. Activities can be seen as a chain of interactional conditions, under which the necessary data is collected: acting, experiencing, encountering, sharing and finally, discreet discussion of what happened and what is perceived. This leads furthermore to reflective working of a therapist and forming more whole conception of the client’s situation and the elements related. When summing up an initial assessment period and drawing up conclusions, therapist uses several sources of information. The process of gaining understanding is constructive, and in an ideal situation the whole multidisciplinary team can take advantage of the cumulative knowledge of initial assessment in music therapy.