[incr Tcl], written by Michael McLennan, is a Tcl extension that adds support for object-oriented programming. Loosely based on the syntax of C++, it provides support for encapsulating Tcl code into classes that can be instantiated as objects.

[incr Tcl] is not part of the core Tcl/Tk package, but can be obtained for free at http://www.tcltk.com/itcl. This chapter covers Version 3.0. [incr Tcl] provides the foundation for [incr Tk], which is discussed in Chapter 8, [incr Tk].

In general, [incr Tcl] is intended to make it easier to develop and maintain large programs written in Tcl and to support Tcl extensions.