It is clear now that proteins lacking ordered structure, generally known as intrinsically disordered proteins (IDPs), possess numerous biological functions that complement functional repertoires of ordered proteins. IDPs are common in nature, and abundantly found to be involved in the pathogenesis of various diseases. These proteins participate in various biological processes and play crucial roles in regulation of functions of their binding partners. Often, disorder-to-order transition induced by the IDP binding to a specific partner defines the low-affinity - high-specificity signaling interactions. Although many IDPs undergo a disorder-to-order transition upon binding, large fraction of IDPs can preserve significant amount of disorder even in their bound states. IDPs can participate in one-tomany and many-to-one interactions, where one intrinsically disordered protein region (IDPR) binds to multiple partners potentially gaining very different structures in the bound state, or where multiple unrelated IDPs/IDPRs bind to one partner. Binding functions of IDPs and IDPRs are controlled by various means, such as numerous posttranslational modifications and alternative splicing. Some of the aspects of the intrinsic disorder-based protein interactions and modes of their regulation are considered in this review.