There are an unknown (but probably very Iagre) number of small dwellingswhich have been built as completed units by governments and their agenciesor flats In multi-storey walk-up blocks. As their occupants require addi-tional or where cultural norms demand different internal layouts, thedwellings are subject to alteration and extension by the occupants. This isusually against building and planning regulations, and, where the unit isstill rented, contravenes tenancy agreements.The effect of transformation activity is to change an ordered, if probablyrun-down, environment into one which Is more chaotic, but usually morecared-for. Housing which was once uniform, of one tenure, and uniformlyresidential in use, is now varied in size and quality of unit, in tenure, andincorporates economic and social uses. Services which were provided for afinite and known population are now used by a larger and variable popula-tion. Households who were regarded as only consumers of housing have be-come producers and controllers of housing suitable to themselves and theirpeers.A recent research project, carried out on behalf of the Overseas Develop-ment Administration of Her Majesty's Government, has assembled the rathersparse existing literature on transformation activity in Algeria, India, Co-lombia, Hong Kong, Israel, Libya and elsewhere, and described brief existingcase studies from Egypt, Zambia, Bangladesh and Ghana, to begin to trace the nature and effects of transformations. The cases have not been specially car-ried out for the study, but they present a variety of responses to the oppor-tunities presented by the process. Within the differing circumstances, somefactors which appear to have causative influence on the occurrence of trans-formation activity have been identified. These include the attitude of the lo-cal authority, security of tenure, ability to recover the investment if thehousehold leaves, space around the dwelling, and a lack of, or serious absta-des to, moving to alternative accommodation.Attempts have been made to draw lessons from the literature and case stud-ies in order to focus future work on paths likely to establish patterns ofcausality, to increase the positive effects of the phenomenon, and to mini-mise its negative effects.