Anastacia Lyn Newkirk ( AN-ə-STAY-zhə; born September 17, 1968), known mononymously as Anastacia, is an American singer-songwriter who has released eight albums and sold over 50 million records worldwide, and collecting a total of 227 gold and platinum certifications. Thanks to her distinctive tone she has been described as "the little lady with the big voice." Anastacia defines her musical style as "sprock", meaning a fusion of soul, pop, and rock.

Anastacia began her career in 1983 as a dancer. In 1990, she started her music career as a backing vocalist. In 2000, she released "I'm Outta Love", her debut single, which quickly topped charts worldwide and paved the way for her first album, Not That Kind. The following year, she released her second album Freak of Nature. In 2004, she released her album Anastacia, preceded by the single "Left Outside Alone", which remained number one across European charts for 15 weeks. After switching record labels, she returned in 2008 with Heavy Rotation and in 2012 she released It's a Man's World, an album of covers of male rock songs. In 2014, she released Resurrection. Its lead single was "Stupid Little Things". In 2023, she released Our Songs, an album of English-language reinterpretations of German songs.

The majority of her success and dominance was primarily in Europe, Oceania, Asia, Africa, and South America, while in her home country, the United States, she experienced moderate chart success. Her career had been impacted by personal struggles due to serious illnesses, which she claimed "slowed down her career".