This chapter describes the relatively growth in the prominence of large-scale area-based or community change initiatives (CCIs) which seek to implement strategic and comprehensive responses to the conditions and systems that contribute to and sustain poor outcomes at a community level. These initiatives, also commonly described as 'complex community initiatives' or ''comprehensive community initiatives' or area-based initiatives, are targeted, 'place-based' collaborative change efforts, which focus on specific areas and target populations rather than individuals. The chapter considers role of theory-based evaluation is central to the evaluation of CCIs. It describes the use of and challenges involved in theory-based evaluation approaches to area-based programmes and strategies. The emergent findings from the evaluation helped to inform the ongoing development of the initiative by providing credible evidence on what aspects of the programme were working well. The chapter explores some of the challenges of evaluating CCIs and how the features and principles of theory-based evaluation might be applied to better understand.