The unitard's history lies in the stage. In the early 1900s, models and dancers wore flesh-colored unitards to simulate nudity. While unitards today can be made of most any material and leave the feet exposed, early unitards were thin and covered the whole body, except for the face and hands. Today, dancers and ice skaters can still be seen wearing flesh-colored unitards to simulate skin. The unitard emerged as a swimsuit in 1906, and can be seen in many early films featuring swimmers. (see Reference 2)
The leotard derives its name from the man who invented it, gymnast and acrobat Jules Leotard. In the 1800s, Leotard created the garment for men, but it soon became popular with women in the early 1900s as a swimsuit. Also known as a maillot, the leotard was adopted by acrobats and circus performers and then by showgirls and burlesque performers. For modesty's sake, men were required to wear shorts over their leotards. By the 1960s, however, designers began creating leotard-like lingerie. In the 1970s leotards gained popularity as both mainstream fitness wear and street wear.
Unitards are typically made of spandex and worn with nothing underneath. They can have feet, no feet or foot straps. Their main purpose is still fitness-based, but today, unitards come in many more colors than their original flesh-colored hue. Many dance companies use unitards as their costume of choice when performing modern interpretive dance, because the simple silhouette of an unadorned unitard doesn't distract from the dance in the way that ornate dance costumes can.
Because of the typically high-cut leg openings that leotards have compared to the longer legs of unitards, gymnasts and dancers choose to wear leotards for the ease of mobility they provide. Both men and women wear leotards, though the garments are cut differently. Men's leotards are typically cut lower in the chest and the groin area. While modesty concerns have faded since the early 1900s, some male gymnasts still wear shorts over their leotards today.