4.1 Introduction The financial sustainability of microfinance projects and institutions consists mainly in finding a balance between the profit gained from the projects and the cost of carrying them out. This variable is taken into great consideration by MFIs, donors and investors who bring financial support to microfinance and the various stakeholders. In pursuing the goal of sustainability the conditions are created so that the results obtained may continue over time and, ultimately, so that the initiatives and institutions are self-sufficient from outside contributions. The sustainability of microfinance programmes is traditionally related to the social benefit that derives from them, usually meant, though not exclusively, as the ability to reach the poorest sector of the population. Such concept of ‘depth’ of intervention is called outreach in specialist terminology. The balance between lasting sustainability of microfinance projects and institutions, and the choice of beneficiaries and the products and services to offer, represents one of the most widely discussed dilemmas among microfinance academics and practitioners. This chapter will discuss, first, the definitions of sustainability and outreach, identifying the various meanings of these broad concepts. Then, with regard to the trade-off between sustainability and outreach, the main criteria to be considered when selecting beneficiaries will be outlined. The aim is to clarify whether, and in what way, working with especially poor customers could affect the offer of financial services in terms of sustainability. Finally, this chapter will propose a range of operating and management choices suitable for reconciling the aims of sustainability with those of outreach.