Chief occupations are farming, ferrous metallurgy (iron works), chemicals, leather (footwear), textiles and foodstuffs (dairy products, alcoholic beverages), building material; oil refinery, thermal power plant. The city hosts Zagreb University's Faculty of Metallurgy and the department of the Nautical Faculty.
The long history of urban life (around 2,500 years) and the extremely favourable position on the confluence of three rivers (the Sava, the Kupa and the Odra) have made Sisak a very important town in the history of Croatia. During the Roman Empire, a Christian mortyr St. Quirinus was nearly killed in Siscia and he is today the patron saint of Sisak.
The triangular fortress of the Old Town from the 16th century, well-preserved and turned into the Native Museum, is the main destination of every tourist. The fortress is famous for the glorious victory of the Croats over the Turks in 1593, the first significant defeat of the up-to-then invincible Turkish army in Europe. The Baroque palace (Mali Kaptol) and the classicist palace (Veliki Kaptol), the Old Bridge (Stari Most) over the Kupa, made of bricks, the ethnological park etc. are most frequently visited objects in the town. Sisak has many rich mineral springs (42 °C - 54 °C).
Sports and recreation facilities in the town and the surroundings include mainly the waters and alluvial plains: a public beach on the Kupa; the rivers Kupa, Odra and Sava and their backwaters offer fishing opportunities, and there are hunting grounds in the regions of Turopolje and Posavina. Sisak is the starting point for sightseeing tours around Lonjsko Polje Nature Park.
During World War II, Sisak was also the site of a concentration camp that was part of the large Jasenovac cluster. Sisak was infamous as a concentration camp specializing in the incarceration and killing of Serb, Roma, and Jewish children.