From east to west :

Eastern Time : Universal Time Coordination or UTC (ex-Greenwich Mean Time or GMT) minus 5 hours. Time used from the Atlantic to the Great Lakes.

Central Time : UTC minus 6 hours; from the Great Lakes to 100 degree west longitude.

Mountain Time : UTC minus 7 hours; from 100 degre west longitude to the Rocky Mountains.

Pacific Time : UTC minus 8 hours; time used from the Rocky Mountains to the Pacific.

Concerning Alaska, Hawaii, Porto Rico and Virgin Islands :

Alaska Time: UTC minus 9 hours.

Hawaii : UTC minus 10 hours.

Porto Rico et les Iles Vierges : Atlantic Time - UTC minus 4.

The Official US Time, a very practical tool to know the hour everywhere in the United States.

What time is it when it is noon (12 PM) in New York or in Washington DC?

It is 11 AM in Chicago, 9 AM in Seattle, and 6 PM in Paris, Brussels or Geneve.

Daylight Saving Time :

The idea to shift the time according to the seasons is not new, and was undoubtedly created by Benjamin Franklin in 1784.

Just like a big number of other countries with a lot of seasonal variations and luminosity, the United States of America have adapted the Daylight Saving Time, thus adjusting the official hour of every Time Zone for the seasons of spring, summer, and beginning of autumn.

The change to summer hours in North America was done during the night of the 1st of April, until 2006.

Since 2007, it is decided by the Energy Policy Act of 2005 that :

The change to summer hours will be done on the second Sunday of March, while the winter hours will be applied starting from the first Sunday in November.