The Milan metropolitan area has the 4th highest GDPs in Europe: were it a country, it would rank as the twenty-eighth largest economy in the world, almost as large as the Austrian economy[69] Milan, according to a study by the European Regional Economic Growth Index is the 57th city in Europe for its GDP growth, being surpassed by some other Italian cities such as Rome and Bologna, yet overcoming Florence. Milan has also been described as being the world's 20th best financial city, a far higher result than coming 25th in 2007, as the 10th best business city in Europe, overcoming Geneva, and falling behind Berlin, and as the 13th fastest improving European city, improving by 6%.

The city is the seat of the Italian Stock Exchange (the Borsa Italiana) and its hinterland is the largest industrial area in Italy. It was included in a list of ten "Alpha world cities" by Peter J. Taylor and Robert E. Lang of the Brookings Institution in the economic report "U.S. Cities in the 'World City Network'" (Key Findings, Full ReportPDF (940 KB)), along with Madrid, Seoul, Moscow, Brussels, Toronto, Mumbai, Buenos Aires and Kuala Lumpur.

In the late 12th century the arts flourished and the making of armours was the most important industry. This period saw the beginning of those irrigation works which still render the Lombard plain a fertile garden. The development of the wool trade subsequently gave the first impetus to the production of silk. As in Venice and Florence, the making of luxury goods was an industry of such importance that in the 16th century the city gave its name to the English word “milaner” or “millaner”, meaning fine wares like jewellery, cloth, hats and luxury apparel. By the 19th century, a later variant, “millinery”, had come to mean one who made or sold hats. The industrial revolution in Northern Europe gave a new prominence to the north area of Milan. It sat on the trade route for goods coming over the Alps, and built mills powered by water from the many rivers and streams. In the mid-19th century cheaper silk began to be imported from Asia and the pest phylloxera damaged silk and wine production. More land was subsequently given over to industrialisation. Textile production was followed by metal and mechanical and furniture manufacture.

Today Milan is a major centre for the production of textile and garments, automobiles (Alfa Romeo), chemicals, industrial tools, heavy machinery, book and music publishing. FieraMilano, the exhibition center, had a fair ground known as "FieraMilanoCity", which was dismantled, except for a few remarkable buildings (including the cycle sports stadium, built in the '20s), to be house for an urban development, CityLife, exploiting its vicinity to the city centre. The new fair ground, in the north-western suburb of Rho, which was opened in April 2005, makes the Fiera Milano the largest trade fair complex in the world.