Peat is a soil that is made up of partially rotted remains of dead vegetation, which has accumulated in layers in waterlogged places for thousands of years.

It largely consists of sphagnum moss along with roots, leaves, flowers and seeds of heathers, grasses and sedges. Occasionally the trunks and roots of trees, such as Scots pine, oak, birch and yew, are also present.

There are three main types of bog in Ireland. Blanket bogs consist of a carpet of peat extending over large areas of land. The nutrient supply is obtained from rainfall and there are two types: lowland blanket bogs, which are found in low-lying (below 200m) areas of western counties; and mountain-blanket bogs, which are found in mountainous areas (above 200m) throughout the country.

Raised bogs are dome-shaped bogs which have developed in former lake basins. As with blanket bogs, the nutrient supply is obtained from rainfall. Fens are flat bogs, which are found around lake margins and in waterlogged areas where there is a supply of mineral-rich waters. Generally, raised bogs develop on top of fens, when the mineral-rich water supply is cut off.