The locking shelf insert for use with a refrigerator or freezer is configured for use with a storage device selected from the group consisting of a refrigerator and a freezer. The selected storage device further comprises a storage shelf. The locking shelf insert for use with a refrigerator or freezer is a barrier structure that attaches to the storage shelf. The locking shelf insert for use with a refrigerator or freezer forms a barricade that controls access into the storage space provided by the storage shelf. The locking shelf insert for use with a refrigerator or freezer comprises a first shell, a second shell, and a door structure. The first shell, the second shell, and the third shell combine to form the barricade such that the form factor of the barricade is adjustable. The door structure provides access into the protected storage space formed by the barricade.