In ordinary language, the word “culture” is used in a diversity of senses. In these pages it is used in one of two ways, the one employed being readily understood from the context. In a general sense, culture means the significant beliefs, customary activities and social prohibitions that are peculiar to man (together with the man-made tools, weapons and other material objects that he finds or has found necessary) that modify, limit or enhance in some manner, most of his discernible natural activities due to and arising from his physical animal inheritance and organization. Culture in a specific sense refers to the significant cultural features of a group or period under consideration. For convenience, any cultural activity according to its dominant purpose may be spoken of as belonging to one of three aspects of culture, (a) economic (technological and intellectual); (b) social (and political); and (c) spiritual (religious, artistic and recreational). To lesser degrees, most cultural activities have relationships with the two aspects other than the dominant. Certain prevalent archaeological designations have been changed to remove time implications (e.g. “early” and “late” Woodland to _Initial_ [beginning] and _Final_ [end of an archaeological series]), or to shorten (e.g. “Tennessee-Cumberland” or “Gordon-Fewkes” to _Cumberland_). Technical terms have generally been avoided; but where it has seemed necessary to retain them or to use words in a special sense, they are explained in the text or can be found in the glossary. The terms _pattern_ and _phase_ are those generally employed in the McKern system of classification, for the larger groupings into which it is customary to place the “cultures” as determined from the typology of the artifacts, their association in the assemblage and pertinent data recovered at a site (or local community) with due regard to circumstances of time and location of other sites nearby and over a larger area. The largest unit is the _pattern_ which is made up of a number of _phases_. Cultural divisions smaller than these units are spoken of here as _subcultures_. The approximate relationships of the archaeological units to the broader cultural stages and substages are given in Table I, page 4. The succession and coexistence of the archaeological units is indicated in the diagram “The Stream of Culture”, p. 57. The summary of “Characteristics of the Archaeological-Cultural Units” occurs on pages 70-76. This is a story mainly of Illinois when occupied by American Indians but it would not give a reasonably true picture without showing the known extensions of some of the cultures into surrounding areas and the probable intrusions from outside the state.