A control system for controlling the air/fuel ratio in an internal combustion engine 10, in which an oxygen probe (lambda probe) 13 is arranged in the exhaust gas of the internal combustion engine 10, has a control device 12 for continuous control. The actual value of the air ratio lambda is determined via a measured probe output voltage in conjunction with an at least approximately predetermined probe-characteristic relationship 16 between the value of the probe output voltage and the value of the air ratio lambda associated therewith. After forming the difference of desired value and actual value of the air ratio lambda, the air/fuel ratio is controlled on the basis of this difference. Such a control system is used primarily in order to reduce the total emission of the main pollutant components of the exhaust gas of an internal combustion engine. In particular in the case of an internal combustion engine 10 with catalytic converter arranged in the exhaust gas, a maintenance of the air ratio lambda as accurate as possible necessary for optimum efficiency of the catalytic converter (lambda=1) is assured.