Katharine Hope McPhee (born March 25, 1984) is an American singer and actress. In May 2006, she was the runner-up on the fifth season of American Idol.

Her eponymous debut album was released on RCA Records in January 2007, and debuted at number two on the Billboard 200, selling 381,000 copies (as of December 2010). The album's first single, "Over It", was a Billboard Top 30 hit and was certified gold in 2008. Her second album, Unbroken, was released on Verve Forecast Records on January 5, 2010, and debuted at No. 27 on the Billboard 200. The album featured the single "Had It All", which peaked at number 22 on the AC chart. It has sold 45,000 copies as of January 2011.

Her third album, the holiday-themed Christmas Is the Time to Say I Love You, was released in October 2010. It debuted at number 11 on the Billboard Top Holiday Albums chart, while the single "Have Yourself a Merry Little Christmas" peaked at number 16 on the Billboard AC chart. As of January 2011, this album had sold 23,000 copies. McPhee released her fourth album, Hysteria, in September 2015. She released her fifth album, I Fall in Love Too Easily, composed of jazz standards, in November 2017.

McPhee has an established acting career, initially co-starring in The House Bunny and Shark Night 3D. She portrayed Karen Cartwright, one of the lead roles on Smash (2012–2013). As Paige Dineen, she starred in Scorpion on CBS (2014–2018). Making her Broadway debut in the musical Waitress, McPhee assumed the role of Jenna in 2018, then originated the role in the West End (2019), and subsequently returned to Broadway (2019–2020).