An exhaust system for a lean-burn internal combustion engine, which system comprising: a first catalysed flow-through substrate monolith for use in treating exhaust gas emitted from the lean-burn internal combustion engine, which catalysed flow-through substrate monolith comprising a first washcoat coating and a second washcoat coating, wherein the first washcoat coating comprises a catalyst composition comprising at least one platinum group metal and at least one support material for the at least one PGM, wherein the at least one PGM in the first washcoat coating comprises platinum; or both platinum and palladium at a weight ratio of greater than 2: 1, which is liable to volatilise when the first washcoat coating is exposed to relatively extreme conditions including relatively high temperatures of ≥700°C, wherein the second washcoat coating comprises, for trapping volatilised PGM, at least one metal oxide selected from the group consisting of optionally stabilised alumina, amorphous silica-alumina, optionally stabilised zirconia, ceria, titania, an optionally stabilised ceria-zirconia mixed oxide and mixtures of any two or more thereof, wherein the at least one metal oxide supports one metal, which is palladium, wherein the second washcoat coating is oriented to contact exhaust gas that has contacted the first washcoat coating; a second catalysed substrate monolith comprising a selective catalytic reduction catalyst, which second catalysed substrate monolith is disposed downstream from the first catalysed flow-through substrate monolith; and an injector for injecting nitrogenous reductant into exhaust gas between the first catalysed flow-through substrate monolith and the second catalysed substrate monolith. a first catalysed flow-through substrate monolith for use in treating exhaust gas emitted from the lean-burn internal combustion engine, which catalysed flow-through substrate monolith comprising a first washcoat coating and a second washcoat coating, wherein the first washcoat coating comprises a catalyst composition comprising at least one platinum group metal and at least one support material for the at least one PGM, wherein the at least one PGM in the first washcoat coating comprises platinum; or both platinum and palladium at a weight ratio of greater than 2: 1, which is liable to volatilise when the first washcoat coating is exposed to relatively extreme conditions including relatively high temperatures of ≥700°C, wherein the second washcoat coating comprises, for trapping volatilised PGM, at least one metal oxide selected from the group consisting of optionally stabilised alumina, amorphous silica-alumina, optionally stabilised zirconia, ceria, titania, an optionally stabilised ceria-zirconia mixed oxide and mixtures of any two or more thereof, wherein the at least one metal oxide supports one metal, which is palladium, wherein the second washcoat coating is oriented to contact exhaust gas that has contacted the first washcoat coating; a second catalysed substrate monolith comprising a selective catalytic reduction catalyst, which second catalysed substrate monolith is disposed downstream from the first catalysed flow-through substrate monolith; and an injector for injecting nitrogenous reductant into exhaust gas between the first catalysed flow-through substrate monolith and the second catalysed substrate monolith.