A safety mechanism for a utility knife, including a razor blade mounted in a blade holder slideably mounted in a blade chamber in the housing. The blade holder includes a tab protruding therefrom and is adapted to move between a retracted, blade-stowage position in the housing and a deployed position wherein the blade at least partially protrudes from the housing. The safety mechanism comprises a foreshortened safety channel adapted to engagingly receive the blade holder tab when the blade holder is retracted into the stowed position. The motion of the tab is restricted by the safety channel, thereby restricting the motion of the blade holder. The tab may be disengaged from the safety channel by simultaneously pushing it away from the deployed position and into the blade chamber. Once the tab is disengaged, the blade holder may be moved into the deployed position by pushing it towards the deployed position while maintaining the pushing force into the blade chamber.

A double-ended dual mechanism retractable blade utility knife. The knife includes two separately actuable mechanisms which allow extension and retraction of one or both blades independently of one another. The cutting surfaces of the respective blades are oriented towards opposite sides of the knife, thereby facilitating rotation of the knife within the user's hand in order to change which blade is currently being used. The independent nature of the dual mechanisms allows both of the blades to be held in the extended position. A storage area is further provided behind each of the mechanisms for the storage of spare blades.