Foundation types refer to the various methods used to support a building or structure. The choice of foundation depends on factors like soil type, load-bearing requirements, and environmental conditions. Common types include shallow foundations, which are placed close to the ground surface, and deep foundations, which extend deeper into the soil to reach stable layers. Shallow foundations include spread footings and slab-on-grade designs, suitable for lighter structures. In contrast, deep foundations, such as piles and caissons, are used for heavier buildings or in areas with poor soil conditions. Each type plays a crucial role in ensuring the stability and longevity of a structure.