TCL or Tcl may refer to:

• Tcl (Tool Command Language), a computer programming language
• Terminal Control Language, used to program VeriFone devices
• Tiny Core Linux, a minimal Linux operating system
• Tymshare Conversational Language, a former experimental interactive language
• Transaction Control Language, a family of computer languages used by database systems to control transactions
• The Common Link, a KOMpatible bulletin board system for MS-DOS
• Transform, clipping, and lighting, a feature of 3D graphics cards
• Think Class Library, a class library for Macintosh featured in THINK C
• tCL, CAS latency in RAM timings

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.