This paper presents a phonetic theory based on physiological parameters. The motivation for and requirements of a phonetic theory are first considered. The theory assumes, without restatement, various known facts from physical and biological science. Certain essential components of the speech mechanism are defined in a set of preliminary definitions. Assumptions about the actions of the vocal mechanism which directly underlie the theory are next presented in a set of axioms. Following the axioms is an extensive set of definitions that specifies the concepts of phonetics and their relationships. A phonetic chart presents the various physiological speech parameters and their values. These parameters include the primary and secondary phonetic parameters and the prosodic parameters. The chart includes a phonetic diagram which presents a basic phonetic symbolization according to the values of the primary parameters. Secondary parameters implicit in the symbols of the diagram are shown in a second chart. The individual parameter values for the various parameters are next defined. The article presents a basic theory of the parameter values and the dynamics of speech production, and also presents a systematic symbolization for descriptive phonetics.