An engine system, comprising: a lean burning active ignition internal combustion engine, comprising: an engine block including plural cylinders; an air handling system including an intake manifold adapted to provide charge air to the cylinders; an exhaust manifold; an active ignition source; and a fuel injection system, which together with the air handling system is adapted to provide a mixture fuel from the injection system and charge air from the intake manifold such that an air-to-fuel ratio of the charge air/fuel mixture in each of the engine cylinders is substantially greater than a stoichiometric quantity to achieve a lean burn condition; and an exhaust gas aftertreatment system (12; 120; 220) fluidly coupled to an outlet of the exhaust manifold, said aftertreatment system (12; 120; 220) including: an oxidation-reduction catalyst; a selective catalytic reduction catalyst fluidly coupled to the oxidation-reduction catalyst and positioned downstream of the oxidation-reduction catalyst; characterized in that the engine system further comprises: a first bypass valve fluidly connected upstream of the oxidation-reduction catalyst, the first bypass valve controllable to route exhaust gas to bypass the oxidation-reduction catalyst, at least in part, under the lean burn condition; and a second bypass valve fluidly connected downstream of the oxidation-reduction catalyst and upstream of the selective catalytic reduction catalyst, the second bypass valve controllable to route the exhaust gas to bypass the selective catalytic reduction catalyst, at least in part, under a stoichiometric operating condition. a lean burning active ignition internal combustion engine, comprising: an engine block including plural cylinders; an air handling system including an intake manifold adapted to provide charge air to the cylinders; an exhaust manifold; an active ignition source; and a fuel injection system, which together with the air handling system is adapted to provide a mixture fuel from the injection system and charge air from the intake manifold such that an air-to-fuel ratio of the charge air/fuel mixture in each of the engine cylinders is substantially greater than a stoichiometric quantity to achieve a lean burn condition; and an exhaust gas aftertreatment system (12; 120; 220) fluidly coupled to an outlet of the exhaust manifold, said aftertreatment system (12; 120; 220) including: an oxidation-reduction catalyst; a selective catalytic reduction catalyst fluidly coupled to the oxidation-reduction catalyst and positioned downstream of the oxidation-reduction catalyst; characterized in that the engine system further comprises: a first bypass valve fluidly connected upstream of the oxidation-reduction catalyst, the first bypass valve controllable to route exhaust gas to bypass the oxidation-reduction catalyst, at least in part, under the lean burn condition; and a second bypass valve fluidly connected downstream of the oxidation-reduction catalyst and upstream of the selective catalytic reduction catalyst, the second bypass valve controllable to route the exhaust gas to bypass the selective catalytic reduction catalyst, at least in part, under a stoichiometric operating condition. an engine block including plural cylinders; an air handling system including an intake manifold adapted to provide charge air to the cylinders; an exhaust manifold; an active ignition source; and a fuel injection system, which together with the air handling system is adapted to provide a mixture fuel from the injection system and charge air from the intake manifold such that an air-to-fuel ratio of the charge air/fuel mixture in each of the engine cylinders is substantially greater than a stoichiometric quantity to achieve a lean burn condition; and an oxidation-reduction catalyst; a selective catalytic reduction catalyst fluidly coupled to the oxidation-reduction catalyst and positioned downstream of the oxidation-reduction catalyst; characterized in that the engine system further comprises: a first bypass valve fluidly connected upstream of the oxidation-reduction catalyst, the first bypass valve controllable to route exhaust gas to bypass the oxidation-reduction catalyst, at least in part, under the lean burn condition; and a second bypass valve fluidly connected downstream of the oxidation-reduction catalyst and upstream of the selective catalytic reduction catalyst, the second bypass valve controllable to route the exhaust gas to bypass the selective catalytic reduction catalyst, at least in part, under a stoichiometric operating condition. a first bypass valve fluidly connected upstream of the oxidation-reduction catalyst, the first bypass valve controllable to route exhaust gas to bypass the oxidation-reduction catalyst, at least in part, under the lean burn condition; and a second bypass valve fluidly connected downstream of the oxidation-reduction catalyst and upstream of the selective catalytic reduction catalyst, the second bypass valve controllable to route the exhaust gas to bypass the selective catalytic reduction catalyst, at least in part, under a stoichiometric operating condition.