Method for initializing a sensor fusion system when booting up or starting the sensor fusion system, wherein the sensor fusion system comprises a base system (101, 201), which is in the form of an inertia navigation system (101, 201), and at least one correction system (103, 104, 203, 204), which is in the form of a global satellite navigation system (104, 204) and/or an odometry navigation system (103, 203), wherein respective measured values are recorded by the base system (101, 201) and by the at least one correction system (103, 104, 203, 204), wherein the measured values directly or indirectly describe physical variables, wherein the measured values are each afflicted by error values, wherein the error values describe deviations of the measured values from the described physical variables, wherein at least the physical variables indirectly described in the measured values of the base system (101, 201) include a speed and/or a position and/or a receiver clock error of the global satellite navigation system (104, 204) and/or a receiver clock error drift of the global satellite navigation system (104, 204) and said variables and the error values thereof cannot be determined during the initialization of the sensor fusion system and wherein the measured values are continuously fused to form a fusion data set after the initialization has concluded, characterized in that, for at least one of the physical variables indirectly described in the measured values of the base system (101, 201) and the error values thereof, starting values are determined from the measured values of the at least one correction system (103, 104, 203, 204) during initialization, wherein the starting values for the error values are determined as variances based on the measurement inaccuracies of the at least one correction system (103, 104, 203, 204), wherein the error values are identified and corrected by means of an error state space filter (105, 205), in particular by means of an error state space Kalman filter (105, 205). wherein the sensor fusion system comprises a base system (101, 201), which is in the form of an inertia navigation system (101, 201), and at least one correction system (103, 104, 203, 204), which is in the form of a global satellite navigation system (104, 204) and/or an odometry navigation system (103, 203), wherein respective measured values are recorded by the base system (101, 201) and by the at least one correction system (103, 104, 203, 204), wherein the measured values directly or indirectly describe physical variables, wherein the measured values are each afflicted by error values, wherein the error values describe deviations of the measured values from the described physical variables, wherein at least the physical variables indirectly described in the measured values of the base system (101, 201) include a speed and/or a position and/or a receiver clock error of the global satellite navigation system (104, 204) and/or a receiver clock error drift of the global satellite navigation system (104, 204) and said variables and the error values thereof cannot be determined during the initialization of the sensor fusion system and wherein the measured values are continuously fused to form a fusion data set after the initialization has concluded, characterized in that, for at least one of the physical variables indirectly described in the measured values of the base system (101, 201) and the error values thereof, starting values are determined from the measured values of the at least one correction system (103, 104, 203, 204) during initialization, wherein the starting values for the error values are determined as variances based on the measurement inaccuracies of the at least one correction system (103, 104, 203, 204), wherein the error values are identified and corrected by means of an error state space filter (105, 205), in particular by means of an error state space Kalman filter (105, 205).