Today, indicators are produced and used worldwide: across all levels and sectors of society, by public, private and civil society actors, and for a variety of purposes, ranging from knowledge provision to administrative control. Ultimately, the tendency towards greater use of indicators is part of broader trends in public policy, notably performance management and evidence-based policy, within what is variously called ‘governance by numbers’, ‘management by numbers’ in public service or ‘numbers discourse’. Amongst the multiple intended functions of indicators in policymaking, the chapter concentrates on their role as tools of policy formulation in various policy venues. Particular attention is given to the distinction between the use and the influence of indicators, and the various unintended and systemic consequences from the production and use of indicators. In policy formulation, indicators can be crucial in characterizing the current situation and framing and conceptualizing problems; constructing future scenarios; identifying and shaping policy solutions; and assessing, comparing and justifying potential policy options. In short, by quantifying and simplifying, indicators render problems more manageable. Yet simplification is itself a source of ‘complication’ to the extent that it can lead to various unintended, systemic consequences that extend beyond the tasks of policy formulation. The broader systemic impacts of indicators can occur through processes such as control, learning and various ‘symbolic’ functions.