Soile Marja Isokoski (born February 14, 1957) is a Finnish lyric soprano. She is an opera singer as well as a concert and lieder singer.
Isokoski was born in Posio, Finland. She graduated from the Sibelius Academy in Helsinki (a cantor-organist diploma, a singing teacher's degree and a singing diploma) and made her concert debut there in 1986.
Isokoski won the Lappeenranta song competition in Finland (1987), the Elly Ameling Competition in the Netherlands (1988), and the Tokyo International Singing Competition (1990). In 1987 she was a finalist in the BBC Singer of the World competition in Cardiff.
She worked first as a church musician in Northern Finland. In 1987 she was engaged as a soloist with the Finnish National Opera and stayed there until 1994. Her first appearance there was as Mimi in Puccini's La bohème in 1987.
Isokoski has sung at all the leading opera houses in Europe, including the Vienna State Opera, Théâtre du Châtelet, Opéra Bastille, La Scala, Deutsche Oper Berlin, Berlin State Opera, Semperoper, the Hamburg State Opera, and the Cologne Opera.
She made her début at the Metropolitan Opera as the Countess in The Marriage of Figaro in 2002. The New York Times wrote on January 28, 2002: "Ms. Isokoski... touched on the Countess' sense of abandonment by the Count without diminishing her regal bearing or the graceful humor she must contribute to the second act. And her dark, burnished soprano should make her a good addition to the Met roster."