States of affairs raise, among others, the following questions: What kind of entity are they (if there are any)? Are they contingent, causally efficacious, spatio-temporal and perceivable entities, or are they abstract objects? What are their constituents and their identity conditions? What are the functions that states of affairs are able to fulfil in a viable theory, and which problems and prima facie counterintuitive consequences arise out of an ontological commitment to them? Are there merely possible (non-actual, non-obtaining) states of affairs? Are there molecular (i.e., negative, conjunctive, disjunctive etc.) states of affairs? Are there modal and tensed states of affairs? In this volume, these and other questions are addressed by David M. Armstrong, Marian David, Herbert Hochberg, Uwe Meixner, L. Nathan Oaklander, Peter Simons, Erwin Tegtmeier and Mark Textor.