Some modern televisions are described as HDTV while others are referred to as 'HDTV Ready'. The difference is that a genuine HDTV has an in-built HD tuner while one that is merely HD ready does not and may sometimes be called a 'HDTV Monitor'.

You need a HDTV tuner in order to be able to receive high definition TV signals through an aerial. With no tuner available, it is necessary to have a separate set-top box for either cable or satellite TV. In these cases, if your cable or satellite service gives all the channels you need, you may be able to save money by getting a HDTV monitor that doesn't have an integrated tuner.

If you do want to get channels through an aerial and your HDTV doesn't have an in-built tuner, you'll need to connect the set to a separate HDTV Tuner. A tuner will generally provide an electronic programme guide (EPG) so that you can see what programmes are available. This may cover several days ahead for all channels and you may be able to set reminders for programmes that you want to see.

All HDTV is digital only and an old-style analogue TV won't be able to display HDTV programming, which uses video compression. Connecting an analogue TV to a digital tuner will allow it to receive both standard and high definition digital broadcasts, although the latter won't have the expected detail due to the TV's display limitations.

Many countries are undergoing a full switch-over from analogue to digital TV, with some still going through the transition and others already complete. The change means that old analogue TVs can no longer receive programming and so either have to be replaced with a digital set or have to be connected to a TV tuner. In the UK, this comes in the form of a freeview box that gives access to a number of free to air channels while in the US it's a digital converter box that allows continued access to TV programmes.

All modern HDTVs should have an integrated tuner. Indeed, in the US, all new TVs are legally required to have a built-in tuner that enables high definition programmes to be received through an aerial. However, there is a loophole in the law that allows a TV to be sold as a monitor, meaning it has no tuner at all. In these cases, it's necessary to connect an external tuner for over the air programmes or a set-top box to get a cable or satellite service.