"The Shag"       Beach Music
The  exact origin of the Shag aren't known, but it's generally considered a form of Southern swing dance, influenced by jazz, blues and gospel music.

The dance's popularity soared on the coast of the Carolinas in the 1940s and '50s, especially along the Grand Strand. The shag had its origins in black nightclubs and was done to R&B music. Young white dancers crossed racial boundaries by going to the clubs to watch dancing. They took the dance to the old Myrtle Beach Pavilion and the old Pad at Ocean Drive, now part of North Myrtle Beach.
Since 1984, it's been South Carolina's official state dance. North Carolina adopted shagging as a state dance in 2005.
The Carolina shag is a swing dance that shares many moves with “jitterbug,” east coast swing, and west coast swing -- not to be confused with Surf Music. The 60s riffs of the Rip Chords, the Ventures, and Jan & Dean were perfect for twisting in the sand, but far removed from shag dancing.
The Chairmen of the Board, the  Kings of the Carolina beach music  scene, define the soul sub-genre --  shag.
1."Give Me Just A Little More Time,"                 Chairmen of the Board
2."Be Young, Be Foolish, Be Happy"
              The Tams
3."What Kind Of Fool Do You Think                   I Am"      Bill Deal & the Rhondells
4."Gimme Little Sign"
              Brenton Wood
5."Teasin' You"
              Willie Tee
6."Girl Watcher"
             The O'Kaysions
7."With This Ring"
             The Platters
8."I Got Loaded"
             Lil' Bob and the Lollipops
9."Um, Um, Um, Um, Um, Um"
             Major Lance
10.       "Get On Up"
             The Esquires

   Beach music is usually a slow groove that's easy to partner-dance to, and tends to be poppier and happier than the usual gutbucket soul of the South. It has origins in New Orleans Soul from the early Sixties, early doo-wop, and can also incorporate some garage-rock sounds.

      "Double Shot Of My Baby's Love" by the Swinging Medallions is a favorite, as is Billy Ward and his Dominoes' "Sixty Minute Man." The Carolina shag may be danced to classic “beach music” tunes such as “Carolina Girls,” “Under the Boardwalk,” and “I Love Beach Music,” or the Carolina shag may be danced to Motown and blues.  Most shag music is interchangeable with west coast swing music written in 4/4 time.

    However, beach music is usually defined as brassy, easygoing pop-soul with a very sweet leading edge: the group Chairmen of the Board, famous for their genre-defining 1970 single "Give Me Just A Little More Time," are considered the kings of this style, with the Tams -- famous for 1963's "What Kind Of Fool (Do You Think I Am)" -- coming in a close second.  Together, the two singles could be seen as benchmarks  to the beginnings of the "beach music" sound.
Shag Activities
The city of year-round shag is the birthplace of the shag: North Myrtle Beach, South Carolina. In particular, the Mecca of shag is a small section of North Myrtle Beach called Ocean Drive Beach. In the Ocean Drive section of North Myrtle Beach, several nightclubs cater to shaggers, providing the beach music and the slick hardwood dance floors they desire.

In particular, Fat Harold’s and Ducks are true-blue shag bars and both feature large hardwood dance floors and a great dance environment. In addition, other clubs such as the O.D. Café and the O.D. Pavillion offer shag activities.

The two biggest annual events on the shag/beach calendar happen, naturally, in South Myrtle Beach, SC, and those are the April Spring Safari and the Fall (September) Migration.  For a list of other national shag events:  shagdance.com. Competitions are held at most events; the biggest shag competition in the US, however, is held at the annual USA Grand Nationals, a combination swing/shag event. There is a Shag Hall of Fame in Myrtle Beach, SC.
Carolina shag is very popular all over the southeast region of the United States; most beach resorts have shag clubs.

In the last ten years, shag and west coast swing have started to merge and many shag steps are being incorporated into west coast swing dance routines.

The music tempo and style of shag is the same as is used in west coast swing. This allows west coast swing and shag dancers to share the same hardwood dance floor.
West Coast Shag is on the upswing >
The shag is a smooth, graceful dance with an emphasis on footwork rather than on turns.  Unlike the jitterbug, shag does not have bounce. Instead, it’s smooth and grounded.

The old saying is that shag is danced from the waist down. Shag emphasizes footwork patterns and patterns that are matched between the two partners. These matched steps are called mirror steps. The partners are typically connected with one hand only, rarely with two hands as is common in jitterbug. Historically, shag tended to spotlight the male dancer, but this is starting to change. Carolina shag uses the same footwork as east coast swing: triple step, triple step, rock step. Some dancers use a “kick-ball-change” step in place of the rock step.
Beach Music opened-up a brand new market for personal appearances; black groups suddenly found a whole new audience, a subculture of southern white kids at the very moment the 1964 Civil Rights Act became law.  
Want to learn to shag? Watch a video and check out more photos at MyrtleBeachOnline.com
Clay Cole; additional material from Robert Fontenot - About.com Oldies, and Walter Edgar's "South Carolina Encyclopedia."
CD at About.com