Art therapy seems to be a highly preferred and satisfactory form of preventive and rehabilitative work for participants in different contexts from education to psychiatry. It consists of multiple theoretical and practical approaches that vary depending of clients’ needs and therapists training, but they are all based on the influences of artmaking within a therapeutic relationship and joint interaction between therapist and client. This doctoral dissertation focuses on analysing clients’ descriptions of art therapy processes and on defining which ingredients are influencing on the qualities of these experiences. In addition, it aims to clarify, which impacts clients experience as personally significant after participating in art therapy. Previous research has not focused on the systematic observation of those experiences that clients describe as challenging during the art therapy process or on developing theoretical models for contextualising those ingredients that are crucial in aiding or hindering therapeutic change. In current research, these aspects are approached from multiple directions including the observation of both individual and group art therapy practices in the context of either adult education or psychotherapy. This research comprises four articles, enabling different methods and data sets to be triangulated. Thus, both the participants’ rich descriptions of art therapy process and its impacts can be analysed from multiple theoretical perspectives. These include different experiential aspects such as embodied sensations and perceptions, emotional and mental experiences as well as intersubjective and dialogical aspects. Of the four articles, the two case studies allow deeper analysis of the unique qualities in individual narratives, while the two systematic content analyses enable shared themes to be found from numerous participants’ descriptions.In this research, the facing-up to, working through and conscious reflection on unpleasant experiences, such as difficulties in art-making, challenging emotions and interaction, turned into important helping processes which aided change. Additionally, based on the findings of a single case study, qualitative change in art making from cognitive control into spontaneous playful processing can be significant in aiding the transformation of previously painful experience into ones that are emotionally manageable and in increasing resources for self-regulation. However, hidden or un-expressed experiences of vulnerability or incapability in relation to verbal expression, art-making or therapeutic tasks and goals turned into hindering ingredients that stagnated the therapeutic process and change. Unpleasant emotions that remain unsolved could arise during sensory interaction in art-making or in social interaction, and a fear for others’ interpretations could prevent or restrict expressing personally important issues. The results of the research create a clearer and better structured understanding of how crucial it is for the experienced outcome of art therapy to encounter and reflect those intrapersonal, intermediate and interpersonal experiences, which awake unpleasant emotions during the process. In addition, as a result of the current study, six themes were recognised in clients’ experiences of significant outcomes: (a) Art therapy increased insights and skills of self-reflection, (b) enabled experiences of self-expression and flow that gave resources for everyday life, (c) increased awareness and handling of emotions, (d) gave experiences of social support and acceptance, (e) increased understanding of self and others, and (f) enabled handling of the past and reflecting on the future. The findings of the current study reveal, how the distinct ingredients that influence the art therapy process are described by different clients and which impacts multiple participants experience as significant after their participation in art therapy. As a result of the study, these findings are contextualised by applying the notion of a triangular working alliance to the individual cases and by developing a new kind of triangular pyramid model to picture the working alliance and aiding or hindering processes in group art therapy. Furthermore, a transtheoretical model for art therapy practice which integrates both essential art based premises and psychotherapeutic core processes is constructed and described in the theoretical part of the research summary. Thus, this research creates both new kinds of theoretical models for exploring the influencing processes in art therapy as well as offers tools for therapeutic practices. It constructs increased understanding of clients’ perspectives on art therapeutic change and its failings both within the context of experiential groups in adult education and in individual art psychotherapy.