Maritime archaeology can be divided in a three-tier hierarchy, of which the first tier consists of the archaeology of shipwrecks and wreck sites. In this discipline the wrecking process itself is studied: how does a ship break up, how does a ship float to the bottom, and how do the remains of both ship and cargo decay over time?The second tier studies the ship as a machine, both in itself and in a military or economic system.The third tier consists of the archaeology of maritime cultures, in which nautical technology, naval warfare, trade and shipboard societies are studied.

Maritime archaeology has two important advantages over land archaeology. First the remains of ships and cargoes, even organic materials, are sometimes better preserved under water or in bottom sediments. The second advantage lies in the fact that until recently, shipwrecks were usually beyond the reach of human intervention or salvage, thereby creating perfect time capsules.

Prior to the industrial era, travel by water was regularly easier than over land. As a result, marine channels, crossable rivers and sea crossings shaped the trade routes of historic and prehistoric civilizations. For example, the Mediterranean Sea was known to the Romans as the inside sea because the Roman Empire spread around its coasts.
The famous record as well as the remains of harbours, ships and cargoes, testifies to the volume of trade that crossed it. Afterward, nations with a strong maritime culture such as the United Kingdom, Holland, Denmark, Portugal and Spain were able to establish colonies on other continents. Wars were fought at sea over the control of important resources.

There are important differences in the continued existence of archaeological material depending on whether a site is wet or dry, on the nature of the chemical atmosphere, on the occurrence of biological organisms and on the dynamic forces present.
Saltwater is particularly unfavorable to iron artifacts including metal shipwrecks, and sea organisms will readily consume organic material such as wooden shipwrecks. On the other hand, out of all the thousands of potential archaeological sites destroyed or grossly eroded by such natural processes, occasionally sites survive with exceptional preservation of a related collection of artifacts.

Maritime archaeology studies prehistorical objects and sites that are, because of changes in climate and geology, now underwater.Bodies of water, fresh and saline, have been important sources of food for people for as long as we have existed. It should be no surprise that ancient villages were located at the water's edge. Since the last ice age sea level has risen as much as 400 feet (~120 meters).Therefore, a great deal of the record of human activity throughout the Ice Age is now to be found under water.

Not all maritime sites are underwater. There are many structures at the margin of land and water that provide evidence of the human societies of the past. Some are deliberately created for access - such as bridges and walkways.Archaeological sites can also be found on the foreshore today that would have been on dry land when they were constructed. An example of such a site is Seahenge, a Bronze Age timber circle.

• Bronze Age

The earliest boats discovered date from the Bronze Age and are constructed of hollowed out logs or sewn planks. Vessels have been discovered where they have been preserved in sediments underwater or in waterlogged land sites, such as the discovery of a canoe near St Botolphs. Examples of sewn-plank boats include those found at North Ferriby and the Dover Bronze Age Boat which is now displayed at Dover Museum. These may be an evolution from boats made of sewn hides, but it is highly unlikely that hide boats could have survived.

Ships wrecked in the sea have probably not survived, although remains of cargo (particularly bronze material) have been discovered, such as those at the Salcombe B site. A close collection of artefacts on the sea bed may imply that artefacts were from a ship, even if there are no remains of the actual vessel.

Late Bronze Age ships, such as the Uluburun Shipwreck have been discovered in the Mediterranean, constructed of edge joined planks. This shipbuilding technology continued through the classical period.

Underwater Archaeology is that branch of the regulation and science of Archaeology that is practiced under water, either by archaeologists outfitted with breathing equipment or by the remote control of machines. Strictly, this means archaeology under water, which is the main discipline of maritime archaeology.

Underwater archaeology is considered as a branch of maritime archaeology (the archaeology of aquatic vessels and associated infrastructure), though not exclusively: underwater excavation techniques and methodology can also be applied in the study of sunken settlement and committal sites, for instance. underwater or maritime archaeology does not essentially deal with wrecks, even if that is the part scuba divers more often deal with.

A prime example of the latter is the ongoing investigation of the remains of Ptolemaic Alexandria in Egypt by Franck Goddio, amongst others.