The Quad Cities are four cities which flank the Mississippi River in Iowa and Illinois in the midwestern United States. They are:

As a patchwork of similarly located but politically different urban units situated at the edge of the Rust Belt, the Quad Cities area serves as an interesting case study on the effects of various economic, social, political, and environmental variables on the trajectory of municipalities seeking economic recovery. Seen as a single urban mass, the Quad Cities perfectly exemplifies the multiple nuclei model of urban arrangement.

The Quad Cities area is one of the few places in the country where telephone companies cooperate with regional phone calls. Iowa and Illinois have different area codes (563 and 309 respectively), yet one can call into either area code, from anywhere in the metro area, by dialing just a 7-digit number. This helps the bi-state area promote itself as a single community, "joined by a river."

The Quad Cities are served by Quad City International Airport, located in Moline. The airport also markets itself to surrounding areas as an alternative to larger airports, such as those in Chicago.

The Roman Catholic Diocese of Davenport serves the Iowa portion of the Quad Cities as well as the southeast quarter of Iowa. This diocese has its headquarters in Davenport. The Diocese of Peoria serves the Illinois portion of the Quad Cities.

Davenport, Rock Island,and Moline were originally called the Tri-Cities. In the 1950s the name Quad-Cities began to emerge in community and business titles, as East Moline became the fourth community to be designated as part of the city-group in this bi-state region. In the 1960s, Bettendorf, Iowa, later gained prominence as its population passed East Moline, but the name "Quint Cities" never caught on, even though several business groups promoted it. For example, KSTT, a very popular local AM radio station, used 'Quint Cities" in several of its station ID jingles and advertising. There are still a few local businesses that bear the name Quint-Cities and others even maintain the original Tri-Cities designation. Yet, it is the Quad-Cities that the area is most widely known as, and while largely a bedroom community, Bettendorf has replaced East Moline as one of the primary anchors, despite signs in East Moline reading "One of the Quad Cities".