This project concerns the analysis of some of the properties and circuit applications of the double barrier resonant tunneling diode. probabilities of the electrons through the diode heterostructure are calculated and an estimation of the tunneling time is obtained using a matrix method. The variation of the tunneling time as a function of the diode dimensions and potential height is investigated. Impedance measurements were carried out on one of these devices and used to estimate the diode's switching speed. This turned to be much higher than the intrinsic tunneling time because of the effect of lumped elements (R, L and C) associated with the diode. A PSPICE compatible model for the diode, based on its I-V characteristic, is proposed and used in simulations of a number of circuits including high frequency oscillators and frequency multipliers.