Archaeology is the study of the human past through material remains such as artefacts (i.e. objects), structures (e.g. standing and ruined buildings, fences, roads), features (e.g. ditches, mounds, canals, landfill), and even whole landscapes modified by human activity, starting from earliest human times through to the present. This is what differentiates archaeology from other historical disciplines - the use of physical evidence in addition to other sources such as written information. Something does not need to be old or a ruin to be of interest to archaeologists!
Archaeologists divide themselves in various ways to indicate their area of interest - sometimes geographical, sometimes by culture and sometimes by time period. Historical Archaeology focuses on the ‘recent' past, usually the last 500-600 years, which means that there is often not only an archaeological (physical) record, but also a documentary (written) and even oral historical and eyewitness records available to us. Historical Archaeologists survey and excavate sites, as well as work in laboratories analysing the artefacts they have recovered just like other archaeologists, but they also spend time in the archives, or interviewing people about their recollections or stories about the past.
The question usually asked is why archaeology is necessary in periods for which there is a documentary record. The simple answer is that not everything was recorded, and even when there are comprehensive documentary records these are often implicitly or explicitly biased to one point of view, selective in what they describe and how they describe it. Literacy was often the preserve of the rich, so archaeology can often provide a voice to individuals and groups whose history is not preserved in documents. Even quite recent events, such as the ‘Cold War' or the ‘Space Race' from the 1950s onwards are often poorly documented (perhaps deliberately), meaning the surviving sites (bunkers, launch pads, radar stations) are some of our best, and only, sources of information.
For the Australasian region (Australia, New Zealand, New Guinea and the near Pacific) which has had indigenous occupation from as early as 60,000 years ago, Historical Archaeology generally covers the period from c.1500 A.D. onwards, when European and Asian cultural groups first began to explore the area and also leave written records of their activities and observations. Consequently, one of the most important themes covered by Historical Archaeologists for the region is the nature of contact between the different cultural groups. Some of the other themes popularly investigated include:
Industrial Archaeology is a subset of historical archaeology, looking at the evolution of industrial processes, workforces and communities, mostly from the 1700s onwards. Maritime Archaeology is another closely allied field, focusing on the relationships between humans and water, including shipbuilding, maritime industries (whaling, sealing, fishing, pearling), ports and harbours, maritime workers and communities.
Historical archaeologists are also concerned with the conservation, management and interpretation of important places, and most professional archaeologists work within the heritage field.