Grey's Anatomy season 2 has 27 episodes. It originally aired on ABC from September 25, 2005, through May 15, 2006, making it substantially longer than the show's first season.
The season follows Meredith Grey, Cristina Yang, Izzie Stevens, Alex Karev, and George O'Malley as surgical interns at Seattle Grace Hospital. Its major storylines include Meredith's complicated relationship with Derek Shepherd and Addison Montgomery, Cristina's pregnancy and relationship with Preston Burke, and Izzie's bond with heart-transplant patient Denny Duquette.
A common source of confusion is that four episodes were originally produced for the first season but aired during the second season's broadcast run. That scheduling history still leaves season 2 with 27 officially counted episodes. The season is also remembered for the two-part bomb-scare storyline, the arrival of Mark Sloan, and the emotional Denny storyline, all of which helped establish Grey's Anatomy as a major network drama.