Digital technology means television signals can be transmitted more efficiently, freeing up more space for more channels and services.
The signals are converted into a digital format and compressed, allowing several digital channels to be carried instead of a single analogue channel.
Viewers will need to decode the signals with a set-top box or integrated digital TV (iDTV) set.
If you can watch BBC Three or BBC Four, you already have digital TV.
Digital TV brings a wider range of services. The BBC, ITV and Channel 4 all provide extra channels for digital viewers, such as ITV2 and More4.
Interactivity means you can use digital TV to take part in polls, buy goods and enjoy enhanced coverage of live events.
Viewers with the right equipment may also be able to watch high-definition television (HDTV) broadcasts as well.
Switching off analogue TV will also improve services for people who watch digital TV through their aerials.
You do not need to pay monthly subscriptions to get digital TV.
The simplest way is through your aerial, with a set-top box, or a TV with a box built-in, for the basic Freeview service of up to 30 channels.
Set-top boxes cost around £50, although you may need to upgrade your aerial to get the best reception.
Sky also offers over 120 free channels through a satellite dish, for a one-off £150 payment. The BBC and ITV are developing a rival Freesat service.
If you want more channels, it's easy to buy extra digital TV services to expand your choice of viewing.
Freeview viewers whose equipment takes a card slot can get a selection of extra channels through Top Up TV.
Through satellite, Sky's entertainment, sports and movie channels have millions of subscribers across the UK.
Digital TV is also available as part of cable packages, and may also be available through your telephone line. Both these options vary across the UK.
Starting in 2007, the old analogue TV signal will be switched off, as digital switchover gets underway.
One area of the UK at a time will switch to digital, starting with Whitehaven, Cumbria. The rest of ITV's Border region will follow in early 2008.
Westcountry, Wales, and Granada are next, in 2009, with the West region, Grampian and Scottish switching in 2010.
The Central, Yorkshire and Anglia regions will switch in 2011, with Ulster, Tyne Tees, Meridian and London the last to lose analogue TV in 2012.
People over 75 and those with disabilities will be eligible for a support scheme, which will provide equipment and help installing it.
The poorest households will get help with digital switchover for free, others may have to pay a fee.
A government-backed "tick" logo will feature on equipment which will work after the UK's switch to digital TV.
Digital UK has been set up by the TV industry to manage the process. It has a consumer helpline: 0845 6 50 50 50.