Intrinsically disordered proteins (IDPs) are strongly represented in functional roles that involve binding interactions with other proteins, such as signaling and regulation. Experimental studies of IDP binding, while challenging, have in recent years increasingly enhanced our understanding of the principles and mechanisms that IDPs employ to interact with their partners. We give an overview of experimental techniques that can be used to study IDP binding, and we attempt to classify experimentally characterized IDP interactions according to three distinctive parameters: level of structure formation and dynamics in the complex, length of the interacting segment(s), and valency. We then review the experimental literature with regard to properties that have been described as characteristic for IDP binding, such as affinity and specificity, as well as association and dissociation rates. We also comment on mechanistic questions such as whether IDP binding is mediated more by conformational selection or by induced fit, and whether folding upon binding of an IDP is encoded in its sequence or templated by the partner.