Abstract: Theft-resistant enclosure systems may include an enclosure having an enclosure interior. An enclosure door may be carried by the enclosure. The enclosure door may be selectively positional in opened and closed positions and selectively lockable in the closed position. At least one enclosure mount member may extend through the enclosure interior of the enclosure. At least one anchoring device may anchor the at least one enclosure mount member outside the enclosure interior of the enclosure. At least one enclosure mounting assembly may be disposed in the enclosure interior of the enclosure. The at least one enclosure mounting assembly may secure the enclosure to the at least one enclosure mount member. Theft-resistant enclosure installation methods are also disclosed.