'Grenzsicherung' was a German pair of directives issued by the Oberkommando der Wehrmacht with the object of securing Germany’s borders against attack (1939).

'Grenzsicherung Ost' (border security east) of April/May 1939 was designed to ensure the security of Germany’s eastern borders against the possibility of Polish and/or Soviet air attack, while 'Grenzsicherung West' of 18 January 1939 was the precursor of 'Verteidigung West' and, as such, designed to ensure the security of Germany’s western frontier against French surprise attack through the use only of locally available forces and thereby buy time for full German mobilisation.