ICI is a C-like, high level language originally developed by Tim Long and placed into the public domain. ICI marries C's expression syntax, control structures and overall feel, with a dynamic, garbage collected, object-based, data model. Version 4 incorporates numerous performance enhancements, refinements to existing features and new features including native support for threads, a cleaner, more well defined API for extension module authors and those embedding ICI within other programs, and new documentation that is superior to that provided in previous releases. ICI is typically used as a scripting-like language in the fashion of Perl, Python, Ruby, Lua, TCL and other such languages. ICI can be called from C and the language itself can be extended allowing applications to provide domain specific functions, types and operators for use in their ICI programs. Embedding within applications allows application authors to make use of ICI's efficient object system which provides many useful facilities. ICI is in the public domain, there is no copyright on it. WWW: http://www.zeta.org.au/~atrn/ici/