Indicators/indices monitor progress toward goals and targets, inform planning and decision-making, raise awareness, and improve communication on sustainability debates. A literature search revealed that, at present, thousands of indicators are available that assess different targets of sustainability under specific conditions that may not work universally. The indicators may assess a single target (non-integrated), a group of targets (integrated), or energy and matter flow. Since sustainability is a complex, multifaceted, and multidisciplinary process integrating the environment, economy, and society, the non-integrated indicators (NIIs) are not suitable for assessing the sustainability of natural and economic systems. Different governmental and non-governmental agencies (UN, EPA, EU, World Bank) have developed integrated indicators that provide a system’s sustainability status. However, since there are numerous interlinkages and relationships between the various targets and goals and between different environmental, social, and economic domains, a precise analysis of what the indicators are measuring is required. This chapter discusses the properties of various integrators that will help select appropriate indicators for assessing sustainability.