Abstract: A lockout device (12) operable to lock a valve (8) into a particular operating position and to prevent further actuation of the valve (8) until removed. The preferred lockout device (12) comprises two lock couplings (16,18), two lock plates (20,22), and two keys (24,26). Each lock coupling (16,18) presents first contact surfaces (40) and is threadably located upon and secured by a set screw (30,32) to an actuator shaft portion (14) of the valve (8) at shaft locations corresponding, respectively, to open and closed valve positions. Each lock plate (20,22) presents second contact surfaces (42) and is stationarily secured relative to the shaft (14) and operable to slidably pass the shaft (14) and receive a corresponding lock coupling (16,18). The keys (24,26) are substantially wedge-shaped and held parallel to one another by a spacer (38).