Barbara Stanisława "Basia" Trzetrzelewska (Polish: [ˈbaɕa tʂɛtʂɛˈlɛfska] ^ⓘ; born 30 September 1954), better known mononymously as Basia, is a Polish singer-songwriter and recording artist noted for her Latin-inspired jazz-pop music.

She began singing professionally in various Polish bands beginning in the late 1960s and during the 1970s, then moved to the UK in 1981. She rose to fame as a singer in the British trio Matt Bianco. By 1986, Basia and her bandmate Danny White had left the group to focus on her solo career.

She signed with Epic Records and enjoyed a successful international career from 1987 until 1995, particularly in the U.S., where her first two albums Time and Tide and London Warsaw New York both sold more than a million copies. Her biggest hits include "Time and Tide", "New Day for You", "Promises", "Baby You're Mine", "Cruising for Bruising", and "Drunk on Love". She also developed a following in Asia.

She took a lengthy hiatus due to personal tragedies. She made a comeback to regular recording and performing beginning with the release of the Matt Bianco reunion album Matt's Mood in 2004. She releases her music through independent labels.

Basia was born in Jaworzno, Poland on 30 September 1954. She had three siblings–two brothers and a sister–and her parents ran a popular ice cream parlor in the town's centre. Growing up in a musical household, Basia enjoyed singing from an early age and had an extensive collection of vinyl records. Her mother played piano and gave her first music lessons.

In 1969, Basia performed as a vocalist in a local band, Astry, appearing with them at the National Festival of Beat Avangarde in Kalisz where they won. Always good at exact sciences, Basia had intended to study mathematics at the Jagiellonian University, in Kraków but eventually took up physics. During her first year at university, Alibabki, a popular Polish all-female band asked her to join the group. Basia accepted the offer in 1972, dropped out of university, and toured with them in Poland and abroad, mostly in Eastern Bloc countries, until 1974. In 1976, Basia took part in the National Festival of Polish Song in Opole as a soloist to no success. From 1977 to 1979, she performed in Polish rock band Perfect.

Moving to London with her partner in January 1981, Basia recorded demo tracks for various artists. She met Danny White (brother of jazz guitarist Peter White) there and his collaborator Mark Reilly by answering their ad in Melody Maker. The trio performed in 1983 as Bronze, but later changed the name to Matt Bianco. Their debut album Whose Side Are You On? was released in 1984 and turned out to be a hit in Europe. It spawned Matt Bianco's UK Top 40 singles "Get Out of Your Lazy Bed" and "Half a Minute".

Despite the success, Basia and Danny White left Matt Bianco in 1985 to focus on Basia's solo career, marking the beginning of a long-term collaboration. Their first release was the single "Prime Time TV" in 1986, a minor success in the UK and Germany. Basia's first solo album, Time and Tide, was released in 1987, selling well in France but performing poorly in the rest of Europe. Accompanying singles "New Day for You" and "Promises" were also only modest successes. The album fared much better in the US where it found popularity on smooth jazz radio stations. The song "Time and Tide" was Basia's first hit on Billboard Hot 100, peaking at No. 26 in 1988, followed by "New Day for You" and "Promises", both reaching the top 10 on the Adult Contemporary chart in 1989. The album was certified platinum by the Recording Industry Association of America in November 1989 selling one million copies in the US alone. Worldwide, it sold almost two million copies.