SISC is an extensible Java-based interpreter of the algorithmic language Scheme. It uses modern interpretation techniques and handily outperforms all existing Java interpreters (often by more than an order of magnitude). In addition, SISC is a complete implementation of the language. The entire R5RS Scheme standard is supported. This includes a full number tower including complex number support and arbitrary precision integers and floating point numbers, proper tail recursion, hygienic macros, and full support for first-class continuations (not just the escaping continuations found in many other systems).