Previous research has shown that different providers of social welfare tend to provide complementary services at a local level, but that there is no complete task specialisation. This means that elements of complementarity theory are challenged, especially the so-called 'principle of matching', i.e. that actors only undertake tasks which match their characteristics. The aim of the present study was to explore complementarity between Swedish local authorities and voluntary organisations in their support for relatives of older people. Interviews were carried out with 55 politicians, civil servants and representatives of voluntary organisations drawn from four municipalities. These municipalities were selected from a sampling frame that ensured representation of different combinations of high and low levels of voluntary and statutory services. Qualitative analysis of interview transcripts showed that, while local authorities are seen as responsible for the support for relatives, voluntary organisations are expected to be complementary, offering 'the icing on the cake', i.e. social support and activities which are regarded as less demanding. Overall, substantial support for a norm of complementarity was found. It is argued that, if those who are active in social policy and voluntary work at a local level agree with the ideal of complementarity, this will influence their wish to arrange activities and services. Therefore, the complementarity norm - rather than the principle of matching - influences the outcome in terms of service provision.