A closing device for windows and doors adapted to be operatively interposed between a panel and a frame of a window and door to retain or lock the panel in a closing condition of said window and door , said closing device comprising: - a striker adapted to be mounted on the frame and comprising a magnetic abutment system, - a lock comprising a lock body adapted to be mounted on the panel and a latch housed in the lock body and comprising a magnetic closing system, wherein said latch is movable along a direction of motion (X) between a retracted position and at least an extracted position with respect to the lock body , the movement of said latch along a closing direction (X) from the retracted position to the extracted position being caused by the magnetic interaction between said magnetic abutment system and said magnetic closing system, - a front wall , wherein in a locking configuration of said front wall , a cavity of said striker is accessible through a front opening for receiving an end portion of said latch and generating a mechanical interference adapted to lock said panel in the configuration of use of the closing device, wherein said striker comprises said front wall which is movable between a locked position corresponding to said locking configuration and a retaining position corresponding to said retaining configuration, and wherein in a retaining configuration of said front wall , said front wall closes said front opening and defines an abutment surface of said striker through which said magnetic interaction adapted to retain said panel operates in the configuration of use of the closing device, characterized in that , said front wall is adapted to selectively assume one from among said locking configuration and said retaining configuration with respect to said striker , therefore by setting the configuration of the front wall the extracted position of the latch with respect to the striker is set, the set configuration being maintained during normal use of the window and door. - a striker adapted to be mounted on the frame and comprising a magnetic abutment system, - a lock comprising a lock body adapted to be mounted on the panel and a latch housed in the lock body and comprising a magnetic closing system, wherein said latch is movable along a direction of motion (X) between a retracted position and at least an extracted position with respect to the lock body , the movement of said latch along a closing direction (X) from the retracted position to the extracted position being caused by the magnetic interaction between said magnetic abutment system and said magnetic closing system, - a front wall , wherein in a locking configuration of said front wall , a cavity of said striker is accessible through a front opening for receiving an end portion of said latch and generating a mechanical interference adapted to lock said panel in the configuration of use of the closing device, wherein said striker comprises said front wall which is movable between a locked position corresponding to said locking configuration and a retaining position corresponding to said retaining configuration, and wherein in a retaining configuration of said front wall , said front wall closes said front opening and defines an abutment surface of said striker through which said magnetic interaction adapted to retain said panel operates in the configuration of use of the closing device, characterized in that , said front wall is adapted to selectively assume one from among said locking configuration and said retaining configuration with respect to said striker , therefore by setting the configuration of the front wall the extracted position of the latch with respect to the striker is set, the set configuration being maintained during normal use of the window and door. <EOS>