"New Archaeology represents a precipitate, unplanned and unfinished exploration of new disciplinary field space, conducted with very varied success in an atmosphere of complete uncertainty. What at first appeared to be merely a period of technical re-equipment has produced profound practical, theoretical and philosophical problems to which the new archaeologies have responded with diverse new methods, new observations, new paradigms and new theory. However, unlike its parent, the New Archaeology is as yet a set of questions rather than a set of answers; when the questions are answered it too will be Old Archaeology."
David L. Clarke, 1973.
The theoretical frame at the heart of processual archaeology is
cultural evolutionism. Processual archaeologists are, in almost all cases, cultural evolutionists. It is from this perspective that they believe they can understand past cultural systems through the remains they left behind. This is because processual archaeologists adhere to
Leslie White's theory that culture can be defined as the exosomatic (outside the body) means of environmental adaptation for humans.
 In other words, they study cultural adaptation to environmental change rather than the bodily adaptation over generations, which is dealt with by evolutionary biologists. This focus on environmental adaptation is based on the
cultural ecology and multilinear evolution ideas of anthropologists such as
Julian Steward. As exosomatic adaptation, culture is determined by environmental constraints. The result of this is that processual archaeologists propose that cultural change happens within a predictable framework and seek to understand it by the analysis of its components. Moreover, since that framework is predictable, then science is the key to unlocking how those components interacted with the cultural whole.
 What this all means to processual archaeologists is that cultural changes are driven by evolutionary "processes" in cultural development, which will be adaptive relative to the environment and therefore not only understandable, but also scientifically predictable once the interaction of the variables is understood. Thus one should be able to virtually completely reconstruct these "cultural processes." Hence came the name "processual archaeology". Its practitioners were also called "new archaeologists".
Methodologically, the advocates of the New Archaeology had to come up with ways of analyzing the archaeological remains in a more scientific fashion. The problem was that no framework for this kind of analysis existed. There was such a dearth of work in this area that it led Willey and Phillips to state in 1958, "So little work has been done in American archaeology on the explanatory level that it is difficult to find a name for it".
 Different researchers had different approaches to this problem.
Lewis Binford felt that ethno-historical information was necessary to facilitate an understanding of archaeological context.
 Ethno-historical (history of peoples) research involves living and studying the life of those who would have used the artifacts - or at least a similar culture. Binford wanted to prove that the
Mousterian assemblage, a group of stone artifacts from France during the
ice age, was adapted to its environment, and so Binford spent time with the
Alaska, a people living in conditions very similar to those of France during the period in question. Binford had a good deal of success with this approach, and though his specific problem ultimately eluded complete understanding, the ethno-historical work he did is constantly referred to by researchers today and has since been emulated by many.
The new methodological approaches of the processual research paradigm include
logical positivism (the idea that all aspects of culture are accessible through the material record), the use of quantitative data, and the
hypothetico-deductive model (scientific method of observation and hypothesis testing).
During the late 1960s and into the 1970s, archaeologist
Kent Flannery began championing the idea that
Systems theory could be used in archaeology to attack questions of culture from an unbiased perspective. Systems theory has proved to be a mixed bag for archaeology as a whole. It works well when trying to describe how elements of a culture interact, but appears to work poorly when describing why they interact the way that they do. Nevertheless, Systems Theory has become a very important part of processualism, and is perhaps the only way archaeologists can examine other cultures without interference from their own cultural biases.
As an instance, in the field of
Colin Renfrew, in re-examining
Proto-Indo-European language and making a case for the spread of Indo-European languages through neolithic Europe in connection with the
spread of farming,
 outlined three basic, primary processes through which a language comes to be spoken in a specific area: initial colonization, replacement and continuous development. From some obvious reasoning he proceeded to some radically new conclusions.