Season one of Castle aired March 9 - May 11th, 2009, Monday nights at 10pm on ABC. The first episode is re-airing again this summer Saturday nights at 9pm on ABC (8pm central). If you've missed the episodes, they are available on the ABC site and Hulu. Season two premiered September 21 2009, and the season finale was May 17, 2010. Castle has been renewed for a full third season, 22-episodes.