In Kenya, as in most developing countries, the provision of adequate housing for the urban poor has been an elusive exercise for the past five decades. Since the early 1960s when serious concerns were raised over housing provision for low income groups and the proliferation of slums and informal settlements, various intervention strategies have been applied without much success. The failure of these interventions has been attributed to high costs of implementation hindering their replication, and displacement of targeted beneficiaries by better endowed income groups upon their completion. As a result, the realised moderate density housing has been transforming into multi-storey housing with intense densification. Housing and the built environment in general are realised within the prevailing systems of social, physical, and economic, settings and are influenced by development and urbanization trends. The purpose of this study therefore was to identify, account and document the prevailing systems of settings and the embedded systems of activities in the informal settlements that determine and sustain them in the city of Nairobi, Kenya. The study analysed these systems at the city, the neighbourhood, and the dwelling levels with the objective of establishing relevant systems of settings and their embedded systems of activities appropriate for adaption in the regularization of informal settlements for sustainable housing development for the urban poor in Nairobi. Both qualitative and quantitative research methodology was utilised in this explorative study. The research methodology applied entailed questionnaires, interviews, observations and discussions. Three case study areas were selected representing three different settings for informal settlements namely; informal settlement on government land with minimal level of interventions; community based informal settlement upgraded for rental housing; and site-and-service settlement informally transforming into multi-storey tenements. Theories and concepts that informed this study include Environment-Behaviour Relations, Environment-Attitude Relations, Sustainable Livelihoods, Social, and Market Theories. The study was conducted in Mathare Valley informal settlement of Nairobi which is located approximately six kilometres from the city centre. The settlement was selected because of the varied informalities it hosts in addition to being the oldest informal settlement in the city. The findings of the study show that the social, economic and physical systems of settings are crucial determinants of housing outcomes and determine the location, nature and characteristics of these settlements including the activities they embody at the city, the neighbourhood and the dwelling levels. Similarly, the study shows that the dwellers adapt to the prevailing systems of settings in response to their livelihood constraints, opportunities and capabilities. As a consequence, limitations arising from economic constraints have led to the predominance of rental housing over owner-occupied housing. Limited access to land has led to crowding and densification. Poverty and unemployment has led to uncontrolled commercial activities within residential neighbourhoods. The study recommends that intervention approaches spearheading regularization of informal settlements commence by considering the problem of informal settlements at city level where their recognition and acceptance is important. This should then be related to job opportunities, ease of access to work, and other social amenities. At the neighbourhood and dwelling levels where the two are intertwined, emphasis should be given to maximum utilization of land and development of housing typologies that evolve with economic improvement of the nation. The government and local authorities should still be responsible for infrastructure development whereas private investors encouraged to develop rental housing targeting the low-income groups and on land designated for such purpose by the government. Market forces should be allowed to determine rent levels. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2011.