A locking luer fitting for connecting fluid lines. In one variation the connection interface includes a male luer connector and a corresponding female luer connector. The female luer connector includes a rotatable collar which engages the male luer connector. In another variation the female luer connector includes a cam configured to prevent inadvertent disconnection of the male luer connector. The locking luer fittings described herein may be implemented in various medical and industrial applications where secured fluid line connection interfaces are desirable.