Circular DNA and RNA molecules, distinguished from their linear counterparts by their covalently closed loop structures, have become pivotal in the fields of molecular biology and biotechnology. These molecules, including plasmids, circular RNA (circRNA), and synthetic constructs, exhibit unique stability and regulatory characteristics, making them valuable for various applications. This review delves into the biochemistry and molecular biology of circular DNA and RNA, explores the range of synthetic modifications possible, and discusses their implications for therapeutic and biotechnological applications. Stay curious, stay innovative. I'm Luke McLaughlin. If you would like to learn more about this topic consider reading our full length articles on www.biotechnologyreviews.com Or consider our podcast series on youtube or Spotify at our Biotechnology Reviews Channel. Our articles are also available on our linkedin newsletter Biotechnology Reviews.