A tailings dam is typically an earth-fill embankment dam used to store byproducts of mining operations after separating the ore from the gangue. Tailings can be liquid, solid, or a slurry of fine particles, and are usually highly toxic and potentially radioactive. Solid tailings are often used as part of the structure itself.

Tailings dams rank among the largest engineered structures on earth. The Syncrude Mildred Lake Tailings Dyke in Alberta, Canada, is an embankment dam about 18 kilometres (11 mi) long and from 40 to 88 metres (131 to 289 ft) high. The dam and the artificial lake within it are constructed and maintained as part of ongoing operations by Syncrude in extracting oil from the Athabasca oil sands; it is the largest dam structure on earth by volume, and as of 2001 it was believed to be the largest earth structure in the world by volume of fill.

There are key differences between tailings dams and the more familiar hydroelectric dams. Tailings dams are designed for permanent containment, meaning they are intended to "remain there forever". Copper, gold, uranium, and other mining operations produce varied kinds of waste, much of it toxic, which pose varied challenges for long-term containment.

There are an estimated 29,000 to 35,000 tailings dams around the world with a rate of .011/Mt of world minereal production. (State of World Mine Tailings 2020 www.worldminetailings failures.org. The Responsible Mining Foundation, found that companies have made little or no progress in improving the documentation and safety practices of these ponds.World Mine Tailings Failures has documented that the number of catastrophic tailings dam failures by decade has steadily increased at a statistically significant level since 2000.

Unlike water-retention dams, the height of a tailings dam is typically increased (raised) throughout the life of the particular mine. Typically, a base or starter dam is constructed, and as it fills with a mixture of tailings and water, it is raised. Material used to raise the dam can include the tailings (if their properties are suitable), earthfill, or rockfill. It is increasingly common for barrier systems such as geomembranes to be incorporated into tailings dams. Impermeable barriers can prevent or reduce seepage, thereby increasing the geotechnical and environmental stability of the dam.

There are three types of dam raises, the upstream, downstream and centerline, named according to the relative position of the new crest of the dam to the previous. The specific design used is dependent upon topography, geology, climate, the type of tailings, and cost. An upstream tailings dam consists of trapezoidal embankments being constructed on top, but toe to crest, of another, moving the crest further upstream. This creates a relatively flat downstream side and a jagged upstream side, which is supported by tailings slurry in the impoundment. The downstream design refers to the successive raising of the embankment that positions the fill and crest further downstream. A centerlined dam has sequential embankment dams constructed directly on top of each other while fill is placed on the downstream side for support and slurry supports the upstream side.

Brazil and Chile have banned the construction of upstream dams, deeming them too dangerous, and the fifty or so in the Brazilian state of Minas Gerais will have to be decommissioned by 2035.

The extraction of economic minerals results in an accumulation of tailings on the surface, mostly in tailings ponds, that occupy a large amount of land. Stratification is inherent to sedimentation, as the heavier particles settle before the lighter particles. Yet, tailings can also represent an untapped resource, as many tailings contain valuable secondary minerals. These could be recovered, contributing to the circular economy and reducing the need for new mining operations. Analyzing the mineralogy of tailings can reveal the presence of economically valuable minerals, such as rare earth elements or other metal resources. This is particularly important as global demand for these resources continues to grow. A thorough understanding of tailings stratigraphy helps to identify the most promising areas for recovery and informs processing methods that allow mineral recovery to be maximized while minimizing environmental issues.