This paper presents Smt-Switch, an open-source, solver- agnostic API for SMT solving. Smt-Switch provides an abstract interface, which can be implemented by different SMT solvers. Smt-Switch provides simple, uniform, and high-performance access to SMT solving for applications in areas such as automated reasoning, planning, and formal verification. The interface allows the user to create, traverse, and manipulate terms, as well as to dynamically dispatch queries to different underlying SMT solvers.