A retractable knife (10) includes an elongate handle (11) and a blade holder (22) slidingly mounted within the handle for sliding movements between a retracted position and an extended position. The blade holder is configured for receiving a blade (24). A manually operable blade lock is formed on the holder and including a release member (32) rotatably mounted on the blade holder. The release member having a first portion (32a) projecting beyond the handle and positioned to be actuated by a finger of a user while holding the handle. A second portion (44) is movable with the first portion between a locking position in which the second portion is received with a notch (24c) of a blade (24) and a releasing position in which the second position is removed from the blade notch to a position outside the notch of the blade. A spring (40) normally rotates the release member to move the second portion to the locking position. Actuation of the release member by the finger of the user to overcome the spring moves the second portion to the releasing position and releases the blade.