Nanobodies (Nbs), the variable domains of heavy-chain only antibodies that naturally occur in camelids, are exquisite molecular tools to stabilize dynamic proteins in unique functional conformations. Recent developments in Nb discovery allow to select allosteric Nbs that perturb the distribution of conformational ensembles of protein complexes that mediate signaling, leading to the allosteric modulation of the signals they transmit. Evidence is also accumulating that such conformational specific Nbs do not stabilize new conformational states but rather change the distribution of existing states to allosterically induce transitions, imprinted by the natural ligands of the system.