The interest in chromogenic conjugated polymers that change their visual appearance in response to external stimulus has gained special attention for the devising and developing sensor systems. Polydiacetylenes (PDAs), obtained by topochemical polymerization of self-assembled diacetylene (DA) monomers, encompass extended π-conjugated functionality and absorb light typically in the visible region with a brilliant blue color appearance. The unique property of nanostructured PDA that leads to their application as sensing elements is the occurrence of a color (typically blue-to-red) and fluorescence (non-to-red) changes that take place in response to a variety of environmental perturbations such as heat, solvent, mechanical stress, pH, and specific ligand-receptor interactions. In this symposium, recent advances in the area of nanostructured PDA-based chemosensors, focused on our results, will be presented.