In synthetic biology, synthetic genetic networks are the primary and most researched field. For industrial, medical, and environmental applications, biological networks or circuits offer scalable and modular tools for designing, constructing, and testing synthetic biological systems. The primary objective of this chapter is to introduce and review the latest advancements in the design and application of these devices. Synthetic genetic networks are categorized at the beginning of this chapter, along with their functions and advantages, and disadvantages. Next, three categories—diagnosis, metabolic engineering, and smart therapeutics—are used to present current uses of digital/analog genetic/metabolic circuits. Lastly, a presentation of tools and techniques for implementing various classes of synthetic gene circuits is given, encompassing most of the approaches that have been developed thus far. This chapter provides an extensive review of synthetic networks, including essential tools and techniques for implementing various synthetic gene circuits, offering a concise overview of the innovative approaches developed to date. And for those who want to learn more about this rapidly developing technology, this chapter provides a thorough overview of synthetic genetic circuits and their most recent developments.