Knowledge has been very important wealth to the mankind but there has not a Knowledge Theory existed yet till the present time.An attempt is thus made in the paper to present a foundation of Knowledge Theory that includes a series of basic issues such as the related concepts and definitions

the methods of representation

the measurements

the reasoning and decision rules.It is believed that the establishment of the Knowledge Theory will lay a solid foundation to the unified theory of information

knowledge

and intelligence and that will greatly facilitate the effective utilization of information and knowledge leading to the growth of the research in the field of intelligent machines.