Green software engineering is the discipline of building sustainable software that is carbon-efficient and carbon-aware. Carbon efficiency aims to reduce carbon emissions throughout the software development life cycle. Carbon awareness involves optimizing software to utilize low-carbon energy sources. Building green software involves making energy-efficient choices in architecture and design patterns, algorithms, data structures, programming languages, language runtimes and infrastructure. This leads to lower operational costs, improved performance, and alignment with organizational sustainability goals. The benefits extend to developers, architects, product teams, and enterprises committed to ESG standards, while end users gain faster, more efficient applications. Ultimately, green software engineering helps organizations create resilient, high performing systems that minimize environmental impact without compromising functionality.