The article introduces a new approach to code safety. We present Naccio, a system architecture that allows a large class of safety policies to be expressed in a general and platform-independent way. Policies are defined in terms of abstract resource manipulations. We describe mechanisms that can be used to efficiently and conveniently enforce these safety policies by transforming programs. We are developing implementations of Naccio that enforce policies on JavaVM classes and Win32 executables. We report on results using the JavaVM prototype.