After discussing some general issues that arise when describing the informational context of a game, we introduce the two main types of models that have been used to describe the players’ beliefs (and other informational attitudes) in a game situation: type spaces (Harsanyi 1967–68; Siniscalchi 2008) and the so-called Aumann- or Kripke-structures (Aumann 1999a; Fagin, Halpern, Moses, &amp; Vardi 1995). Although these two approaches have much in common, there are some important differences which we highlight below. A second, more fundamental, distinction found in the literature is between “quantitative” structures, representing “graded” attitudes (typically via probability distributions), and “qualitative” structures representing “all out” attitudes. Kripke structures are often associated with the former, and type spaces with the latter, but this is not a strict classification.