Intrinsically disordered proteins (IDPs) are important components of the cellular signalling machinery, allowing the same polypeptide to undertake different interactions with different consequences. IDPs are subject to combinatorial post-translational modifications and alternative splicing, adding complexity to regulatory networks and providing a mechanism for tissue-specific signalling. These proteins participate in the assembly of signalling complexes and in the dynamic self-assembly of membrane-less nuclear and cytoplasmic organelles. Experimental, computational and bioinformatic analyses combine to identify and characterize disordered regions of proteins, leading to a greater appreciation of their widespread roles in biological processes.