Year Sets - Modern U.S. stamps, anything issued after 1940, are in most cases collected by the year, since individual stamps sell for so little it is not worth a dealer’s time to sell the stamps individually.

Yellowstone National Park - the National Park honored on the five cent National Parks issue of 1934, featuring "Old Faithful"

Yorktown Issue - the bi-colored two-cent stamp of 1931 honoring the Battle of Yorktown and the surrender of General Cornwallis to General Washington.