Synthetic biology leverages genetic parts—modular DNA sequences with defined functions—as fundamental building blocks to engineer novel biological systems. This discipline, rooted in early 2000s initiatives like the Registry of Standard Biological Parts, emphasizes standardization, abstraction, and modularity. Genetic parts encompass diverse functional elements, including promoters, ribosome binding sites, coding sequences, and terminators, each crucial for a genetic system’s overall function. Their precise design and characterization are important for applications in medicine (e.g., engineered cells, biosensors), industrial biotechnology (e.g., microbial factories), and environmental management (e.g., bioremediation). Despite their significance, designing and characterizing genetic parts face challenges like context dependency and biological variability. This chapter explores the principles guiding genetic part creation, contemporary and traditional design methodologies, and characterization techniques for performance measurement of genetic parts and reproducibility. The text also details various genetic part types (DNA sequences, gene products, engineered elements) and their functions. Key design principles like modularity, orthogonality, and predictability are discussed, alongside genetic part design tools for sequence optimization, RNA/protein design, DNA assembly, and high-level modeling.