In this dissertation we consider several limiting criteria forn-dimensional diffusion processes defined as solutions of stochasticdifferential equations. Our main interest is in criteria for polynomialand exponential rates of convergence to the steady state distributionin the total variation norm. Resulting criteria should place assumptionsonly on the coefficients of the elliptic differentialoperator governing the diffusion.Coupling of Harris chains is one of the main methods employed in thisdissertation.