On February 17, 2009 all full-power broadcast television stations in the United States will stop broadcasting on analog airwaves and begin broadcasting only in digital. Digital broadcasting will allow stations to offer improved picture and sound quality and additional channels. Find out more about whether or not you will be impacted by the digital TV
http://www.dtv.gov/
basically if you’re not with a cable provider and you are using just an antennae you may need a converter box for your televsion, but it depends because your tv may already have a digital tuner or hd tuner, etc.