incr Tcl (commonly stylised as [incr Tcl], and often abbreviated to itcl) is a set of object-oriented extensions for the Tcl programming language.

It is widely used among the Tcl community, and is generally regarded as industrial strength [citation needed].

Itcl implementations exist as both a package that may be dynamically loaded by a Tcl application, as well as an independent standalone language with its own interpreter.

Itcl allows namespaces to be used for organizing commands and variables.

incr Tcl from the Ground Up by Chad Smith, published in January 2000.