This chapter establishes the parameters that are useful in describing plasma properties and behavior. Length, mass, and time-related properties are defined. The physics of sheath formation and the significance of the Debye length to boundary sheaths are presented. Plasma oscillations are described and plasma frequency is derived. Magnetic field effects on charged particles and plasma properties are discussed. The collection of electrons and ions by a biased conductor (Langmuir probe) in a plasma is analyzed.