Archaeologists need to know something of the nature of the processes of human land use and cultural development, including the type, extent, duration, and intensity of change resulting from their operation. Natural and human-caused changes on that portion of the archaeological resource base consisting of archaeological sites are explored. History and terminology of the discipline are introduced. Specific concepts such as artifact movement, fire impacts, impacts to soils and sediments, and vandalism of archaeological sites are discussed. See also AATA 19-1120. -- AATA