When she was only fourteen, her modeling agency arranged a reading and audition for a short called 26 Summer Street (released 1996), which she won. Cook also landed a role in the 1995 production of The Baby-Sitters Club based off the widely popular pre-teen book series. Cook continued to capitalize on the family-oriented comedies when she appeared as Becky Thatcher in Tom and Huck (1995). She acted opposite Jonathan Taylor Thomas (a star at the time due to his work on Home Improvement).

Cook began taking more quirky and independent roles when she agreed to act in the 1997 film House of Yes, starring Parker Posey and Freddie Prinze Jr. The film revolved around a mentally unbalanced woman (Posey) who believed she was Jackie Kennedy and who became murderous when learning her brother was engaged. For the next two years, Cook went on to star in numerous film and television productions. Most notably, she appeared in Country Justice opposite George C. Scott, the TV mini-series True Women with Dana Delany and Angelina Jolie, and a very bit part in the 1998 comedy-drama Living Out Loud with Holly Hunter.

Resonating with the pre-teen and teen crowd, Cook and Prinze won numerous awards. Cook won the Blockbuster Entertainment Award for Favorite Newcomer, the MTV Movie Award for Best Breakthrough Female Performance, and the Young Star Award for Best Performance by a Young Actress in a Comedy.

Still playing to the teen crowd, Cook performed a three episode stint on the popular television series Dawson’s Creek. Even with the blockbuster success of She’s All That, Cook still opted to take smaller, more independent roles. In 1999, she co-starred with Elijah Wood in The Bumblebee Flies Anyway, and Sally, a low-budget drama that played with the concepts of reality and fantasy. However, Cook followed with a string of larger budget films such as Get Carter (2000), Antitrust, Blow Dry, Josie and the Pussycats and Texas Rangers (all 2001).

Unfortunately, almost every movie seemed to be another in a string of poorly received films, so Cook reevaluated her approach to filmmaking. She left behind the blockbusters and again opted for independent roles, a trend that continues today. To this end, she made films such as 11:14 (2003), The Big Empty (2003) and My First Wedding (2004). She also appeared in several episodes of the successful television series Las Vegas with James Caan and Molly Sims. Cook is currently in post-production for four films, including Matters of Life and Death and Nancy Drew starring Julia Roberts’ niece Emma Roberts. Cook has also lent her voice talents to several video games and television productions, including the 2006 video game Crisis Core: Final Fantasy VII.

Cook has dated fellow actors Vincent Kartheiser, Ryan Reynolds, Shane West, and Rider Strong. She became engaged to Daniel Gillies in December 2003, and the two wed in August 2004.