Definitions of and judgments regarding effectiveness in social impact assessment (SIA) depend on how the activities that constitute SIA, and the purposes of SIA, are understood. The latter, in particular, are defined differently by various groups and interests that participate in, or are affected by, impact assessment processes. Thus the concept of 'effectiveness', and the issue of what is required to achieve it, are both contested and contextual. This article reviews a number of different approaches to SIA, and outlines in general terms what effectiveness might mean for each. It then considers, at two levels, what 'effective SIA' involves in a specific context, that of large-scale resource development on the traditional lands of Australia's Aboriginal peoples. The first level involves control of SIA. For indigenous peoples who have historically been excluded from and ignored by SIAs undertaken as part of government approval processes, Aboriginal control of SIA is an essential prerequisite for 'effective SIA'. However control only creates the potential for effectiveness. The second level of analysis involves the numerous practical activities that must be undertaken, and issues that must be addressed, to realise this potential. The paper develops a matrix designed to help practitioners and affected indigenous groups identify and manage these activities and issues in a systematic way. Many of them are also relevant in conducting SIA in non-indigenous contexts, and so the analysis is of wider application.