In the paper a new class of output feedback variable structure controllers and state estimators (observers) for uncertain/nonlinear dynamic systems with bounded uncertainties and/or nonlinearities are proposed. No statistical information about the uncertain elements is assumed. A variable structure systems (VSS) approach together with the geometric approach to the analysis and synthesis of system zeros are employed in the synthesis of the proposed output feedback controllers and state estimators. The role of system zeros in the output feedback stabilisation and state estimation, using the VSS approach, is discussed. Numerical examples included illustrate the feasibility of the proposed stabilisation and state estimation schemes.