This chapter explores the basic principles of sustainable finance. It discusses how it has changed over time and how it is different from green finance. This chapter also explains why sustainable finance is becoming more important worldwide. It addresses urgent environmental issues, especially climate change, and stresses the need to reach net-zero emissions by assessing risks and integrating ESG factors. Furthermore, it examines the economic effects of climate change, the expected costs of transitioning to net zero, and the need for new financial solutions to tackle these issues. By identifying important stakeholders and sharing real-world examples, it shows how sustainable finance can promote significant changes in critical infrastructure sectors, contributing to a more resilient and fair future.