Stephanie Lynn Pratt (born April 11, 1986) is an American reality television personality. She is known best for her role as a cast member on MTV's The Hills.

Pratt began her role on The Hills in Season 3, in 2007, as Spencer's angry sister who confronts Lauren Conrad. She eventually apologized to Lauren and became one of her close friends, causing a rift between her and Spencer. In Season 4, Stephanie gained more of a major role, showing more of her personal life and her past drug abuse. In Season 5, Stephanie worked with Lauren at People's Revolution, though she was later fired by Lauren (on Kelly Cutrone's saying.) Pratt became close friends with Audrina and Lo following Conrad's departure and Kristin Cavallari's new role in the series. Even though Pratt and Cavallari came into the series as rivals from an argument about Audrina's ex-boyfriend they soon became best friends.

Despite rumors of not returning after said season, Pratt returned and was featured as a lead role in the sixth and final sesason. Season 6 covered topics and plot lines featuring the cast' life the audience sees in the media, unlike previous seasons. Stephanie talks of her DUI arrest, and her sibling rivalry has elevated to the more serious. It is eventually seen as a cast decision to not mention Heidi or Spencer on the series, since both have drastically changed. The Hills ended its series run on July 13, 2010.

Pratt is the younger sister of Spencer Pratt, and the sister-in-law of Heidi Montag (both of whom are on The Hills.) She has struggled with bulimia in the past due to the pressure to be thin stemming from appearing alongside very thin co-stars on the show.

In April, 2010, Pratt posed nude for PETA's Be Nice to Bunnies iPhone application, which is intended to help the public find stores and products that are kind to animals.

Stephanie Pratt has stated in many public appearances that she has not seen her brother or his wife Heidi Montag in more than a year.

In a 2007 US Magazine interview, Pratt revealed previous substance abuse problems and discussed an incident in which she shoplifted $1,300 worth of merchandise from a Neiman Marcus in Honolulu in 2006, while working as a production assistant on ABC’s LOST.

On October 18, 2009, Pratt was arrested in Hollywood, California, on suspicion of drunk driving and booked into jail in Van Nuys. She took two breathalyzer tests, first blowing 0.08, then blowing 0.09. The legal limit in California is 0.08. She was released several hours later after posting a $5,000 bail.