It　is　well　known　that　[CO3]2−　groups　are　one　kind　of　most　promising　structural　groups　for　nonlinear　optical　(NLO)　materials　in　the　ultraviolet　(UV)　and　visible　spectral　region,　because　their　π-conjugated　planar　triangular　configuration　is　favorable　to　generate　excellent　optical　properties.　There　is　still　no　review　on　NLO　materials　with　[CO3]2−　groups　and　the　corresponding　structure-property　relationships.　In　this　review,　we　systematically　summerize　NLO　materials　with　π-conjugated　[CO3]2−　triangles　and　attempt　to　demonstrate　the　underlying　structure-property　relationships　between　the　microscopic　arrangement　of　[CO3]2−　triangles　and　macroscopic　optical　properties.　There　are　some　interesting　findings　disclosed.　Firstly,　the　cation-centered　MOxF2　(M　=　cations　of　+2　or　+3　oxidation　numbers,　x　=　4,　5,　6,　8)　polyhedra　in　carbonates　play　a　significant　role　in　the　orientation　of　[CO3]2−　groups,　which　make　the　major　contribution　to　NLO　coefficients.　More　concretely,　the　different　radii　of　M　cations　results　in　different　arrangement　of　[CO3]2−　groups.　Secondly,　in　contrast　to　the　notable　anionic　group　theory,　some　cations,　especially　the　cations　with　stereoactive　lone-pair　electrons,　make　additional　considerable　contributions　to　the　overall　NLO　effect.　We　believe　that　this　review　will　shed　helpful　insights　on　the　rational　design　and　synthesis　of　new　NLO　materials　of　carbonates.　©　2019　Elsevier　B.V.