  We describe four approaches here: (1) Features and fluents (Sandewall), (2) Motivated Action Theory (Morgenstern and Stein), (3) State Minimization in the Event Calculus (Shanahan) and (4) Causal Theories (Lifschitz and others). The accounts of the first three in what follows will be fairly brief; fortunately, each approach is well documented in a single reference. The fourth approach is most likely to be interesting to philosophers and to contain elements that will be of lasting importance regardless of future developments in this area.