Marine construction is the process of building structures in or adjacent to large bodies of water, usually the sea. These structures can be built for a variety of purposes, including transportation, energy production, and recreation. Marine construction can involve the use of a variety of building materials, predominantly steel and concrete. Some examples of marine structures include ships, offshore platforms, moorings, pipelines, cables, wharves, bridges, tunnels, breakwaters and docks. Marine construction may require diving work, but professional diving is expensive and dangerous, and may involve relatively high risk, and the types of tools and equipment that can both function underwater and be safely used by divers are limited. Remotely operated underwater vehicles (ROVs) and other types of submersible equipment are a lower risk alternative, but they are also expensive and limited in applications, so when reasonably practicable, most underwater construction involves either removing the water from the building site by dewatering behind a cofferdam or inside a caisson, or prefabrication of structural units off-site with mainly assembly and installation done on-site.^{[citation needed]}

Some aspects of the marine environment that complicate construction:

The geology of the seabed has a strong influence on almost any marine structure. The seabed is the substrate on which the structure must stand, and both the morphology and the material affect the design and construction. It is therefore necessary for accurate and reliable geological surveys to be made before a construction project can be started. There have been developments in sampling of seabeds but some soils remain difficult to analyse and sampling may not produce results as accurate as would be desired. In-place strength may be greater than conventional sampling methods indicate, and sampling methods may not recover and identify critical constituents due to insufficient sampling. Failure to identify potential problems can lead to delays and cost overruns. Many marine structures cover extensive areas, and the soil properties may vary considerably. Cost and time constraints may make it difficult to gather sufficient samples from borings to fully describe the substrate. Other methods for remote substrate analysis may identify potential variations for closer examination.

Bottom material is often sedimentary, and in deeper water, may range from extremely fine, low density silts to loose gravels, to dense, highly compacted sands. Granular sediments may be subject to liquefaction if strongly disturbed, as by earthquakes, cyclic impact of storm waves, or crushing by sea ice. When this occurs the soil can behave like a dense liquid. This can also happen during some construction processes, such as piledriving. The presence of large boulders in glacial till deposits can give a misleading impression of bedrock, hiding the further extent of softer sediment below.

In arctic regions, permafrost can form an unreliable foundation, and deeply buried clathrates can be a problem when drilling, but are usually too deep to be a problem for construction.

Methane can occur at shallow depths in delta sediments with significant quantities of organic matter, and in arctic silts. These van reduce the shear strength of silty and clay soils. A sudden, large release may temporarily reduce water density sufficiently to cause vessels or drill rigs to sink, and can cause an explosion or fire at the surface.

Clays may initially support a steep slope when excavated, but are subject to creep and sudden large-scale collapse when subjected to shock loads or vibration.

Unconsolidated sand – seasonal shifts.