Aims: To synthesise and evaluate evidence about experiences of psychotherapy environments. Methods: Studies were identified from systematic literature searches of PsycINFO, ASSIA and Web of Science. Selected studies were published in English between 2002 and 2016. Fifteen studies met the inclusion criteria. A quality appraisal process indicated that the quality of evidence was 'moderate' across included papers. Findings: In the narrative synthesis, we use the concept 'mereology' to underscore the mutually constitutive relationship between person, world and practice. In this context, themes of relating, containment and process each highlight the integral and nuanced influences of the environment on the therapeutic endeavour. Conclusions: In therapeutic training, it would be beneficial to utilise the concept of a 'mereological system' (reflecting how a person and their environment shape each other and constitute a whole) to show how environmental features may affect clinical practice. Designers may also benefit from using this concept for the purpose of improving therapeutic environments. Further research that explores features of the therapy as part of a mereological system may pinpoint other aspects that facilitate beneficial therapy outcomes.