The problem of transforming non-linear systems with input disturbances to their linear equivalents is investigated. A characterization of the class of non-linear systems with disturbances that are equivalent to controllable quasi-linear systems with disturbances, ż = Az + bv + ξ(z) d, is given. The necessary transformations (state-space coordinate changes and control input-space coordinate changes by non-linear feedforward and feedback) are presented and their implications for control system synthesis are discussed. Finally a numerical example is given,