Genome reduction can be defined as the systematic removal of non-essential genetic elements to simplify an organism’s whole genome architecture while maintaining cellular functionality. Initially inspired by natural evolution observed in symbiotic bacteria, organelles, and oligotrophic microbes, genome reduction has evolved as a powerful tool in both fundamental research and applied biotechnology. This chapter explores genome reduction not only as a biological phenomenon but also as an engineering strategy to redefine biological systems for improved efficiency, predictability, and utility. The chapter begins by defining genome reduction and outlining its origins in evolutionary biology, followed by a chronological overview of key milestones from early gene deletion experiments to modern synthetic genome projects. Various genome reduction strategies are discussed in detail, including top-down approaches, bottom-up approaches, and hybrid approaches that leverage advancements in genome engineering and computational modeling. The implementation of these strategies across various prokaryotes and eukaryotes is presented in detail, outlining organism-specific implementations, challenges, and applications. Future perspectives highlight the convergence of evolutionary biology, synthetic biology, computational biology, and high-throughput genomic toolkits in accelerating genome design and customization of minimal genomes. Potential applications of genome reduction span the development of industrial microbial chassis and insights into the origins of life. Collectively, this chapter offers a detailed and structural framework for understanding genome reduction and its transformative potential across multiple sectors of biotechnology.