When psychoanalysts and psychotherapists are in a particular mental state, it may happen that visual images come up spontaneously in their minds. When they appear, these unbidden visualizations seem to be unrelated to what is going on in the therapy at the time. This dissertation is a review and analysis of texts published by psychoanalytic practitioners about these events. My research has three related foci: 1) psychotherapists’ clinical descriptions of their inner experience of unbidden visualizations and their reflections on what it is like; 2) the effect and function of unbidden visualizations in the therapeutic process; and 3) psychotherapists’ use of spontaneous images in the therapeutic relationship with their patient. My method of analysis is a critically applied thematic analysis, developed within a hermeneutic-interpretive methodological framework. In this approach themes (patterns of meaning across the data) are conceptualized as integrated networks of subthemes, and the final analysis of interrelationships among major themes is essential. The results are nine major themes, (Personal, inner experience; Disturbance by the unknown; Dream-like perceiving; Sensing and evocatively gathering unsayable complexities; Revealing by giving shape; Care and scrutiny; Togetherness; Intimacy; Generative aliveness) and two dynamic major themes (Tensions of time and temporality; Movement through tension and paradox), eleven in total. These themes reveal that unbidden visualizations are creations of the psychotherapist’s unconscious but intersubjectively activated and motivated by complex unconscious processes in the therapeutic relationship—they are relational events. Unbidden visualizations crystallize central issues and dynamics in psychoanalytic practice and evocatively express visually what is momentarily obscure and unsayable. Furthermore, unbidden visualizations open a triangular mental space between psychotherapist and patient, by functioning as a third object which is created within the psychotherapist-patient dyad but simultaneously experienced as external to it—as an intrusive, sensory mental object and experience. This dissertation ends with a discussion of findings in the context of current psychoanalytic thinking, of clinical implications of findings, and of further research implications.