Proteins may vary from being rigid to having flexible regions to being completely disordered, either as an intrinsically disordered protein (IDP) or having specific intrinsically disordered regions (IDRs). IDPs/IDRs can form complexes otherwise impossible, such as wrapping around the binding partner, hence providing the plasticity needed for achieving assemblies with specific functions. IDRs can exhibit promiscuity, using the same region in the sequence to bind multiple partners, and act as hubs in protein-protein interaction network (an essential part of the cell signalling network). Disorder-to-order transition on binding provides specificity with affinity, optimum for reversibility of the binding, thus offering suitability for regulation and signalling processes. IDRs interactions may be modulated by the environment or covalent modifications; mis-signalling or their unnatural or non-native folding may lead to diseases. This article aims to provide an overview of structural heterogeneity, as seen in IDPs/IDRs, and their role in biological recognition, binding and function.