This paper presents a comprehensive overview of energy efficiency as a modern engineering paradigm in software development. With growing demands on digital infrastructure and increasing energy consumption in information and communication technologies (ICT), optimizing software for energy performance has become a key quality requirement—alongside scalability, performance, and security. Drawing from international standards (such as ISO/IEC 25010), sustainability frameworks (e.g., Green Software Foundation), and relevant scientific literature, the paper analyzes how architectural choices, programming languages, software practices, and toolchains influence energy usage. It further highlights good engineering practices, comparative language benchmarks, and the integration of energy awareness into modern development workflows, such as DevOps and CI/ CD pipelines. The aim is to raise awareness among software engineers and decision-makers about the importance of sustainable software design and to offer practical guidelines for building energy-conscious systems.