The discovery of archaeological sites and artifacts can be separated into three types: 1) planned; 2) accidental; and 3) rescue. A planned excavation occurs when an archaeologist does background research on the site he is interested in and plans the dig. Anyone can be part of an accidental excavation. This occurs when someone stumbles over an artifact (without any previous planning). Rescue excavations are based on a need to quickly collect artifacts before they are destroyed by weather, natural decay, or human intervention.

There are many sub-specialities within archaeology which require different types knowledge and background.

Urban Archaeology

Urban Archaeology usually occurs when land is being cleared for new buildings or older buildings are being torn down. Archaeologists are called to excavate the sites in order to collect and preserve the artifacts. This type of archaeology is many times considered a rescue excavation because of the time pressure of the builders/construction crews.

Industrial Archaeology

The purpose of Industrial Archaeology is to uncover more facts about the activities and events that occured during the Industrial Revolution beginning two hundred years ago.

Underwater Archaeology

Underwater Archaeology is probably the largest sub-specialty and usually requires scuba equipment or specialized submarines to manuever in the water and help with the excavation. Excavations can range from finding sunken treasures to discovering the ruins of Civil War ships to Egyptian ruins in the Nile River

Garbage Archaeology

A modern sub-specialty, Garbage Archaeology tries to learn more about today's society based on what people throw away.

Experimental Archaeology

This sub-speciality tries to help archaeologists make intelligent guesses about their discoveries. They experiment by trying many possible explanations and by using enthnographic analogy(comparing similar artifacts and knowledge from different cultures). For instance, if an archaeologist uncovers a tool and guesses what it was used for, she may actually make a similar tool and using other known objects from the same time, see if it works.