West Coast Swing is a fun, current dance done with a partner to popular music and blues rhythms in a smooth,
sexy, playful style.
Most people who dance WCS spend the majority of their dance time dancing with each other at parties and clubs, and some attend weekend conventions to dance with friends from around the country and the world. Though routines and regular practice partners are a part of the competition scene,
the majority of West Coast Swing is focused on social dancing;
even many of the most impressive and entertaining shows are "Jack and Jill" dancing, in which partners are drawn at random and music is a surprise. 
Like all the other swing dances so popular in the United States, WCS grew out of the swing style of jazz music of the 1920s-1950s, coming into its own as a regionally distinct style of swing dance around the 1940s. Though this dance has a long history, it is a living dance: it is danced to currently popular music, and because of its improvisatory nature, easily incorporates a wide range of movement styles and attention to the sound of the song. More information about WCS can be found on Skippy Blair's website and blog, and on Sonny Watson's website.
The best information about West Coast Swing dancing in the Washington DC area can be found by following this link or this one.
{There are lots of links in this page! It's like a little treasure hunt for my favorite videos. click click!}