Security design, which broadly speaking deals with the issue of designing optimal contractual mechanisms for overcoming various frictions between agents, is the subject of an extensive literature. This paper presents a review of recent work on security design and is organized around the applications of security design in various fields of finance starting with classic corporate finance applications such as capital structure and corporate governance, financial intermediation applications such as securitization and contingent capital, the interaction of market and security design, as well as emerging applications such as fintech, sustainable finance and healthcare finance. Future research is also discussed.