Simple adaptive control techniques have recently been developed for continuous stationary and non-stationary linear systems, based on the fact that the output stabilizability property of systems can be used to realize ‘almost passive’ configurations that may facilitate the implementation of simple robust adaptive controllers. This paper extends these concepts to a class of non-linear systems that are linear in the control; this includes manipulators and similar systems. Since it has recently been shown that non-linear systems that can be stabilized via static or dynamic output feedback become ‘almost passive’ via some corresponding parallel feedforward, a rigorous proof of the robust stability of the simple adaptive control of non-stationary almost passive systems is presented