Abstract Comparison of the transition-metal oxides and sulfides highlights as a common feature the possibility of finding a displacive crystallographic transition at a cross-over from localized to itinerant electronic behavior. In metastable NiS with the B8 1 structure, for example, this cross-over manifests itself as a first-order expansion of the c-axis on cooling from a Pauli-paramagnetic metallic phase to an antiferromagnetic phase at a Néel temperature T N= 264 K. A first-order lattice expansion also occurs in the perovskite NdNiO 3 on cooling from a metallic to an insulating phase, but in this case the magnetic order below T N indicates a segregation into ferromagnetic Ni-O-Ni (111) sheets containing itinerant electrons that are coupled by ionic bonding across an oxide-ion (111) plane to give a charge-density wave (CDW) with a propagation vector q CDW  and a spin-density wave (SDW) with q SDW = 2 q CDW. In rhombohedral FeS, itinerant minority-spin electrons co-exist with localized majority-spin electrons into molecular orbitals. A low-spin to intermediate-spin transition in LaCoO 3 occurs via short-range ordering of low-spin and high-spin to intermediate-spin trivalent cobalt, localized a electrons at the high-spin cobalt transforming to itinerant σ∗ electrons in the intermediate spin state. As a final example, mixed-valent manganese oxides with perovskite structure are chosen to illustrate strong electron coupling to local Jahn-Teller deformations at a cross-over from localized to itinerant electronic behavior of σ-bonding electrons in the presence of π-bonding electron configurations with localized spins S = 3 2 .