A tourniquet for application to a patient's limb in an emergency situation, and a method for its application. The tourniquet includes a tension-sensing mechanism used to establish a baseline tension in a loop around an injured limb, and a tension-increasing mechanism to reduce the circumference of the loop and tighten the tourniquet as required beyond the baseline tension. The tension-sensing mechanism may be incorporated in a buckle in which when sufficient tension is developed in the loop a pin protrudes to engage and maintain tension in a strap member which is part of the loop. A latch may be incorporated in the buckle to keep it in a condition in which the pin protrudes to engage the strap and maintain the baseline tension. A release tab operable to release the latch is located where it is protected against inadvertent operation.