In some cases -- at Lacoste and Michael Angel -- the look bordered on androgynous, while the style was a prelude to more feminine ponytails and updos at shows like Carolina Herrera, Prabal Gurung, DKNY, Cynthia Rowley and Jason Wu.
And at still other collections, like Narciso Rodriguez, the side part curved a little in the back and gave way to glossy, straight hair.
So why a side part, now?
Many shows looked to side parts of the past for inspiration. Side parts were all the rage in the roaring '20s, with flappers favoring gelled-back styles for an androgynous look, which was popular at the time on the heels of women's suffrage. Daisy Buchanan of F. Scott Fitzgerald's epoch-defining book, "The Great Gatsby," was all about the side part, and her character, depicted by Mia Farrow, wore one in the 1974 movie. Both Lacoste and Micheal Angel nodded to the '20s with their collections, and the hair followed suit.
The mod 1960s was another era referenced often in the Spring 2011 collections; a deep side part was favored by style icons like Twiggy at that time.
The smooth, shiny locks at Narciso Rodriguez were inspired by his muse in the 1990's Caroline Bisette Kennedy, who was known for wearing her straight blonde locks in the parted style shown on his runway.
A side part is also a great way to show off your face, and your clothing.
"I chose a simple hairstyle that would unify all the girls so they all looked exactly the same," said hairstylist Eugene Souleiman of the hair at Narciso Rodriguez.
At DKNY, Souleiman wanted the hair "away from the face, not too hard, with a softness, a realness, a looseness," as opposed to the sleek, futuristic look Odile created at Gurung.
At Rowley, the look Bok-Hee produced was certainly sleek, but made more feminine with giant barrettes and Twiggy-style lashes. Carolina Herrera's models also dressed up the look with barrettes spilling down the models' ponytails.
When wearing this style, we suggest pairing it with a bold lip -- classic red or a deep wine are two gorgeous options for Fall 2011 -- a little mascara and an otherwise natural face.
Click here for 15 more amazing hair trends from the Spring 2011 runways.
Another hot trend for Spring 2011? The peach manicure.