Introduction. This present thesis focuses on occupational adaptation in the empirical context of vulnerable populations relative to ageing (Study II, III), disability (Study I, II) and poverty (Study IV) and in a theoretical context (V). Aim. The overall aim was to explore and describe occupational adaptation in diverse contexts with a focus on persons in vulnerable life situations. Methods. The thesis was conducted with a mixed design embracing quantitative and qualitative methods and a literature review. The data collection methods comprised questionnaires (Study I, II, III), individual interviews (Study II, IV), group interviews (Study III) and data base searches (Study V). Altogether 115 persons participated in the studies and 50 articles were included in the literature review. Qualitative content analysis was used to analyse the interviews (Study I, II, III, IV) and the literature review (Study V). Parametric and non-parametric statistics were applied when analysing the quantitative data (Study II, III). Results: Women in St Petersburg, Russia, who have had a minor stroke reported more dependence in everyday occupations than the stroke symptoms indicated and they overemphasized their disability and dysfunction. When the environmental press did not meet their competence, it caused negative adaptive behaviour (Study I). In home rehabilitation for older persons with disabilities, interventions based on the occupational adaptation model was compared with interventions based on well-tried professional experience. The results indicated that the use of the occupational adaptation model increased experienced health and the participants acquired adaptive strategies to manage every day occupations. (Study II). An occupation based health-promoting programme for older community dwelling persons was compared with a control group. The intervention group showed statistically significant improvement in general health variables as vitality and mental health, but there were no statistically significant differences between the groups. A qualitative evaluation, in the intervention group, showed that participation in meaningful, challenging occupations in different environments stimulated the occupational adaptation process (Study III). Occupational adaptation among vulnerable EU citizens begging in Sweden was explored by interviews. The results showed that the participants experienced several occupational challenges when begging abroad. The results show a variety of adaptive responses, but whether they are experienced as positive or negative is a matter of perspective and can only be determined by the participants themselves (Study IV). Finally, the results from a literature review (Study V) showed that research on occupational adaptation was mainly based on Schkade and Schultz’s and Kielhofner’s theoretical approaches. Occupational adaptation was also used without further explanation or theoretical argument (Study V). Conclusion: The surrounding context was shown to play an important role for the participants’ occupational adaptation. There were no general occupational challenges or adaptive responses to the various vulnerable life situations, but some common features in the participant groups’ adaptive responses were found. For example, if the environment put too great demand on the person and social support was lacking, there was a risk of negative adaptation. Moreover, persons with low functional capacity were vulnerable to environmental demands and dependent on a supportive environment for their adaptive response. However, persons living in supportive environments developed adaptive responses by themselves. Further, personal factors needed to be strengthened to meet the demands of the environment. Upholding occupational roles was a driving force in finding ways to adapt and perform occupations. Considering the theoretical context, the occupational adaptation theoretical approaches need to be further developed in relation to negative adaptation and to support use within community-based and health-promotive areas.