This book introduces a new seven-mass biomechanical model for the mechanical vibration of vocal folds. The model is based on the body-cover layer concept of the vocal fold biomechanics, and segments the cover layer into three masses along the longitudinal direction of the vocal fold. The model is used to characterize the vocal fold dynamics of 14 human subjects with healthy and pathological vocal folds (nodule, polyp and unilateral paralysis). A semi-empirical procedure for tuning the model parameters is proposed so that the model response matches as closely as possible the experimental data obtained from high-speed videoendoscopy in the time and frequency domains. Two factors, quantifying the asymmetry between left and right vocal folds and anterior and posterior segments of the vocal folds, are introduced. Based on the value of the asymmetry factors for the 14 subjects, the 2D asymmetry space is subdivided into four regions corresponding to healthy vocal folds, nodule, polyp and unilateral paralysis. This yields a clear visual aid for clinicians, correlating the model parameters to voice quality.