A cable converter box or television converter box is an electronic tuning device that transposes/converts any of the available channels from a cable television service to an analog RF signal on a single channel, usually VHF channel 3 or 4. The device allows a television set that is not “cable ready” to receive cable channels. While later televisions were "cable ready" with a standard converter built-in, the existence of premium television (aka pay per view) and the advent of digital cable have continued the need for various forms of these devices for cable television reception. While not an explicit part of signal conversion, many cable converter boxes include forms of descrambling to manage carrier-controlled access restriction to various channels.

Cable-ready televisions and other cable-aware A/V devices such as video recorders can similarly convert cable channels to a regular television set, but these do not include advanced capabilities such as descrambling or digital downconversion.

A digital television adapter (DTA), or digital-to-analog converter [set-top box], or commonly known as a converter box, it is a television tuner that receives a digital television (DTV) transmission, and converts the digital signal into an analog signal that can be received and displayed on an analog television set. It may refer to over-the-air broadcast television signals received by an television antenna, or to cable TV systems which switched to digital cable. It normally does not refer to satellite TV, which has always required a set-top box either to operate the big satellite dish, or to be the integrated receiver/decoder (IRD) in the case of direct-broadcast satellites (DBS).

In North America, these ATSC tuner boxes convert from ATSC to NTSC, while in most of Europe and other places such as Australia, they convert from Digital Video Broadcasting (DVB) to PAL. Because the DTV transition did nothing to reduce the number of broadcast television system standards (and in fact further balkanized it), and due to varying frequency allocations and bandplans, there are many other combinations specific to other countries.