The Borsa Italiana S.p.A., based in Milan, is Italy's main stock exchange. It was privatised in 1997 and is a part of the London Stock Exchange Group plc since 2007. In 2005, the companies listed on the Borsa were worth US$890 billion. It is also informally known as Piazza Affari ("Business Square"), after the city square of Milan where its headquarters (the Palazzo Mezzanotte building) is located.