The Mississippi River is one of the world’s major river systems in size, habitat diversity and biological productivity. It is also one of the world's most important commercial waterways and one of North America's great migration routes for both birds and fishes.

Native Americans lived along its banks and used the river for sustenance and transportation. Early European explorers used the Mississippi to explore the interior and the northern reaches of what was to become the United States. Fur traders plied their trade on the river and soldiers of several nations garrisoned troops at strategic points, at various times, along the river when the area was still on the frontier.

The Mississippi River is the second longest river in North America, flowing 2,350 miles from its source at Lake Itasca through the center of the continental United States to the Gulf of Mexico. The Missouri River, a tributary of the Mississippi River, is about 100 miles longer. Some describe the Mississippi River as being the third longest river system in the world, if the length of Missouri and Ohio Rivers are added to the Mississippi's main stem.

When compared to other world rivers, the Mississippi-Missouri River combination ranks fourth in length (3,710 miles/5,970km) following the Nile (4,160 miles/6,693km), the Amazon (4,000 miles/6,436km), and the Yangtze Rivers (3,964 miles/6,378km). At a rivers delta, the reported length may increase or decrease as deposition and erosion occurs.

As a result, different lengths may be reported depending upon the year or measurement method. The staff of Itasca State Park at the Mississippi's headwaters suggest the main stem of the river is 2,552 miles long. The US Geologic Survey has published a number of 2,300 miles, the EPA says it is 2,320 miles long, and the Mississippi National River and Recreation Area suggests the river's length is 2,350 miles.At Lake Itasca, the river is between 20 and 30 feet wide, the narrowest stretch for its entire length. The widest part of the Mississippi can be found at Lake Winnibigoshish near Bena, MN, where it is wider than 11 miles. The widest navigable section in the sAt the headwaters of the Mississippi, the average surface speed of the water is about 1.2 miles per hour - roughly one-half as fast as people walk. At New Orleans the river flows at about three miles per hour. But the speed changes as water levels rise or fall and where the river widens, narrows, becomes more shallow or some combination of these factors. It takes about three months for water that leaves Lake Itasca, the river's source, to reach the Gulf of Mexico.shipping channel of the Mississippi is Lake Pepin, where the channel is approximately 2 miles wide. 

Another way to measure the size of a river is by the amount of water it discharges. Using this measure the Mississippi River is the 15th largest river in the world discharging 16,792 cubic meters (593,003 cubic feet) of water per second into the Gulf of Mexico. The biggest river by discharge volume is the Amazon at an impressive 209,000 cubic meters (7,380,765 cubic feet) per second. The Amazon drains a rainforest while the Mississippi drains much of the area between the Appalachian and Rocky Mountains, much of which is fairly dry.

At Lake Itasca, the average flow rate is 6 cubic feet per second. At Upper St. Anthony Falls in  Minneapolis, the northern most Lock and Dam, the average flow rate is 12,000 cubic feet per second or 89,869 gallons per second. At New Orleans, the average flow rate is 600,000 cubic feet per second.

 The Mississippi River drains an area of about 3.2 million square kilometers (1.2 million square miles) including all or parts of 32 states and two Canadian provinces, about 40% of the continental United States. The Mississippi River watershed is the fourth largest in the world, extending from the Allegheny Mountains in the east to the Rocky Mountains in the west. The Amazon for comparison drains about 7.1 million square kilometers (2.7 million square miles).