 With impossible worlds added to a theory, necessarily equivalent expressions no longer have to have the same semantic values. Apart from their widespread use in the semantics for logical systems, work has continued on using impossible worlds for giving theories of psychological attitude ascriptions and of claims about meaning: see Jago (2014) for one recent treatment of a number of issues involving mental content and reasoning. Impossible worlds also help in theories of other kinds of representations: for use in theories of impossible fictions, see Priest (1997) and Badura and Berto (2019). Epistemologists are starting to find applications for impossible worlds in theories of knowledge: see, for example, Melchior (forthcoming). And logicians are using them to model non-omniscient hyperintensional agents by combining impossible worlds semantics with dynamic epistemic logic (Bjerring and Skipper (2019); Solaki, Berto, &amp; Smets forthcoming).