The proposed research investigates adaptive internal model-based and feedforward-based methodologies for the design of controllers capable of securing internal stability and asymptotic tracking of reference trajectories in presence of harmonic disturbances at both the input and output channels of a plant. The research focuses on general classes of multivariable linear systems, and specific classes of nonlinear systems of interests in aerospace and electro-mechanical applications. Particular attention is devoted to the issue of robustness against both parameter uncertainty on the plant model, and uncertainty about the fundamental frequencies of the periodic disturbance. Experimental setups (flexible joint manipulator, 2-DOF helicopter model) are employed to validate the theoretical findings.