Everyone knows that Halloween costumes are outfits worn on or around October 31, the day of Halloween. However, despite popular histories that claim Halloween goes back to ancient celebrations of Samhain, the fact is that there is very little evidence of masking or costuming on Halloween before the twentieth century. In fact costuming became popular for Halloween parties in America in the early 1900s, more often for adults than for children. Furthermore, the first mass-produced Halloween costumes appeared in stores in the 1930s when trick-or-treating was becoming popular in the United States.

What sets Halloween costumes apart from costumes for other celebrations or days of dressing up is that they are most often designed to imitate supernatural and scary beings. Costumes are traditionally those of monsters such as vampires, ghosts, witches, zombies, and devils. There are also costumes of pop culture figures like film, television, and cartoon characters. Another popular trend is for women and in some cases, men, to use Halloween as an excuse to wear particularly revealing costumes, showing off more skin than would be socially acceptable otherwise.

According to The National Retail Federation's (NRF) 2007 Halloween Consumer Intentions and Actions Survey, the top Halloween costumes for adults in the United States are: 1. Witch, 2. Vampire, 3. Cat or Mouse, 4. Princess, 5. Fairy, 6. Wench or Tart, 7. Clown, 8. Angel or Devil, 9. Nurse or Doctor

In Hollywood, celebrities seem to follow the trend as the popularity of Halloween partying rekindles. In recent years we have seen stars like Michelle Trachtenberg and Andrea Parker as very sexy vampires, Christina Aguilera as sexy nurses, Paris Hilton as a bunny, Lindsay Lohan as a dancer from Flashdance, Keira Knightly as a 1920's Flapper Girl, and Brittany Snow as Tinkerbell.

There are also numerous television shows that have a Halloween theme each year and quite often has some of the shows characters in costumes. Pauley Perrette was dressed as Marylin Monroe on NCIS, Julie Benz was dressed as Tomb Raider on Dexter, and Emily Deschanel dressed as Wonder Woman on Bones.

Of course there are also costumes in Hollywood that were not originally intended to have anything at all to do with Halloween but became favorites for Halloween parties. Jeannie from I Dream of Jeannie and Princess Leia from Star Wars are two costumes that pop up every year.

Fans that normally show their love for a particular show or celebrity with the collection of autographs and memorabilia use this time of year to go a step further and actually emulate their favorite characters or celebrities. This type of fan emulation has always been common but as Halloween regains popularity so does the popularity of loyal fans dressing up and displaying their devotion. So, just like autograph or memorabilia collecting dressing up for Halloween can be exciting and fun for fans and flattering for celebrities.