Most `causal' approaches to reasoning about action
have not addressed the basic question of causality: what has to
be the case in the world in order for the assertion `<I>A</I> causes <I>B</I>'
to be valid? Pearl's recent causal theories based on _structural
equations_ do provide an answer to this question. In this paper, we
extend Pearl's formalism so that the typical problems encountered in
common sense reasoning about action can be represented in it. The
resulting theory turns out to be a powerful tool for handling the
ramification problem. It also provides new insights into actions with
non-deterministic and/or `disjunctive' effects and it may  help bridge
the conceptual gap between `causal' and `non-causal' approaches to
common sense temporal reasoning.