This chapter provides an overview of the concept of sustainability by carefully defining what sustainable development is and by describing how sustainability relates to the Triple Bottom Line (TBL), Corporate Social Responsibility (CSR), Environmental, Social and Governance (ESG), and sustainable finance, with specific reference to the Principles for Responsible Investments (PRI). Moreover, the main initiatives launched globally to manage sustainability issues and the regulatory evolution on the topic are described, as well as the role played, and pressure brought by stakeholders. The chapter will end with an introduction to the most widespread types of non-financial reporting (Sustainability Reporting and Integrated Reporting), which will be explored in greater depth in subsequent chapters.