Forced excitation techniques with sinusoidal or random signals are used to measure respiratory mechanical impedance. The real part of this impedance is the effective resistance, and it has been used to characterize mechanical function in a wide assortment of experiments and clinical studies. Others have used linear regression analysis to compute the resistance, compliance, and inertance in a simple series model. This approach provides reliable parameter values in homogenous lungs, but these parameters are difficult to interpret in abnormal inhomogenous lungs. Nonlinear regression approaches have been used but this approach is still developmental. This report reviews these existing forced excitation techniques and data processing schemes, and it also summarizes the current state of development of the method and identifies several issues requiring further development.