This study explores unusual interventions (UIs) in counselling and psychotherapy, as defined by Akhtar (2011, p. xvii): “Clinical surprises ... when the [therapist] makes a radical departure from the set and familiar rules of technique”. There is currently a paucity of literature and research in this area, and the present study aims to contribute to an emerging theory: Under what circumstances do UIs occur, how do they manifest, and what are the therapeutic consequences? A qualitative methodology, constructivist grounded theory (Charmaz, 2006), was used in this endeavour. 10 psychotherapists and psychologists, of varying theoretical orientations and training backgrounds, were recruited via email, and subsequently interviewed about UIs. 2 pilot interviews with trainees were included in the final sample, which, otherwise, consisted of practitioners with a minimum of 10 years clinical experience. The Grounded Theory is comprised of 21 UI proposals, derived from 4 core, sequential categories. A distinction is made between Full and Partial UIs, with the former denoting a spontaneous, ‘not thought through’ therapist response. The UIs reported in this study predominantly had a positive therapeutic effect. The UI process may lead to therapist self-conflict as it represents a deviation from prescribed, standard technique.