Tcl (originally from "Tool Command Language", but conventionally spelled "Tcl" rather than "TCL"; pronounced as "tickle" or "tee-see-ell") is a scripting language created by John Ousterhout. Originally "born out of frustration", according to the author, with programmers devising their own languages intended to be embedded into applications, Tcl gained acceptance on its own. It is commonly used for rapid prototyping, scripted applications, GUIs and testing. Tcl is used on embedded systems platforms, both in its full form and in several other small-footprint versions.

The combination of Tcl and the Tk GUI toolkit is referred to as Tcl/Tk.

The Tcl programming language was created in the spring of 1988 by John Ousterhout while working at the University of California, Berkeley.

Tcl conferences and workshops are held in both the United States and Europe.

Tcl's features include

Tcl did not originally have object oriented (OO) syntax (8.6 provides an OO system in Tcl core), so OO functionality was provided by extension packages, such as incr Tcl and XOTcl. Even purely scripted OO packages exist, such as Snit and STOOOP (simple tcl-only object-oriented programming).