Scheme 48 is an implementation of the Scheme programming language as described in the Revised^5 Report on the Algorithmic Language Scheme. It is based on a compiler and interpreter for a virtual Scheme machine. The name derives from our desire to have an implementation that is simple and lucid enough that it looks as if it were written in just 48 hours. We don't claim to have reached that stage yet; much more simplification is necessary. Scheme 48 tries to be faithful to Revised^5 Scheme Report, providing neither more nor less in the initial user environment. (This is not to say that more isn't available in other environments.)