The present disclosure concerns a method for monitoring the operation of a catalytic converter that is disposed in an exhaust system of an internal combustion engine, in particular of a motor vehicle, wherein an exhaust gas temperature upstream of the catalytic converter and an exhaust gas temperature downstream of the catalytic converter are determined. In order to improve the monitoring of such a catalytic converter regardless of the respective type of catalytic converter used, it is proposed with the present disclosure that an exhaust gas mass flow through the catalytic converter is determined, wherein it is determined whether a thermal inertia of the catalytic converter is present or absent according to the presence of a triggering event taking into account the exhaust gas temperatures and the exhaust gas mass flow.