Method for calibrating a camera system of a motor vehicle, wherein at least one camera (8 - 11) of the camera system sequentially generates camera images (21 - 28) respectively from an environment of the motor vehicle and a computing device of the camera system respectively generates a virtual view of the environment from a predetermined virtual perspective, in particular a plan view of the environment, from the camera images (21 - 28) by means of a projection, characterized by the steps: a) the computing device recognizes a straight vehicle motion of the motor vehicle along a predetermined direction of motion, b) with recognized the straight vehicle motion, the computing device passes at least once a calibration cycle for each camera (8 - 11), in which the computing device performs the following steps: - camera images (23, 24) of the camera are transformed based on current projection parameters of the projection, - motion vectors are determined in the virtual view based on the transformed camera images (23', 24'), - for two geometric characteristics of the motion vectors respective corresponding x and y reference values are set, - an error value is determined from a difference between the two geometric characteristics of the motion vectors and the respective corresponding x and y reference values, and - new projection parameters are determined from the current projection parameters depending on the error value wherein multiple motion vectors are determined by dividing each transformed camera image (23', 24') into a matrix of image blocks adjacent to each other or overlapping and determining a motion vector for each image block wherein in each calibration cycle, the error value is iteratively reduced by determining intermediate projection parameters depending on the error value and newly orienting only the motion vectors in the virtual view based on the intermediate projection parameters by newly transforming by means of the projection, until the error value satisfies a predetermined optimization criterion such that for a y component of each motion vector, the y component being oriented parallel to the vehicle transverse axis, the y reference value zero is set, and for a x component oriented parallel to the vehicle longitudinal axis, an average value of all of the x components of the motion vectors is set as the x reference value, and a sum of the squared differences is formed as the error value. a) the computing device recognizes a straight vehicle motion of the motor vehicle along a predetermined direction of motion, b) with recognized the straight vehicle motion, the computing device passes at least once a calibration cycle for each camera (8 - 11), in which the computing device performs the following steps: - camera images (23, 24) of the camera are transformed based on current projection parameters of the projection, - motion vectors are determined in the virtual view based on the transformed camera images (23', 24'), - for two geometric characteristics of the motion vectors respective corresponding x and y reference values are set, - an error value is determined from a difference between the two geometric characteristics of the motion vectors and the respective corresponding x and y reference values, and - new projection parameters are determined from the current projection parameters depending on the error value - camera images (23, 24) of the camera are transformed based on current projection parameters of the projection, - motion vectors are determined in the virtual view based on the transformed camera images (23', 24'), - for two geometric characteristics of the motion vectors respective corresponding x and y reference values are set, - an error value is determined from a difference between the two geometric characteristics of the motion vectors and the respective corresponding x and y reference values, and - new projection parameters are determined from the current projection parameters depending on the error value