Trivial UTF-8 is a small library for doing UTF-8-based in- and output on a Lisp implementation that already supports Unicode -- meaning char-code and code-char deal with Unicode character codes.

The rationale for the existence of this library is that while Unicode-enabled implementations usually do provide some kind of interface to dealing with character encodings, these are typically not terribly flexible or uniform.

The Babel library solves a similar problem while understanding more encodings. Trivial UTF-8 was written before Babel existed, but for new projects you might be better off going with Babel. The one plus that Trivial UTF-8 has is that it doesn't depend on any other libraries.