A fly system or theatrical rigging system, is a system of lines (e.g., ropes), blocks (pulleys), counterweights and related devices within a theater that enables a stage crew to quickly, quietly and safely fly (hoist) components such as curtains, lights, scenery, stage effects and, sometimes, people (e.g., in "Mary Poppins"). Systems are typically designed to fly components between clear view of the audience and out of view, into the large opening, fly loft (fly space), above the stage.

Fly systems are often used in conjunction with other theatre systems, such as scenery wagons, stage lifts and stage turntables, to physically manipulate the mise en scène.

Theatrical rigging is most prevalent in proscenium theatres with stage houses designed specifically to handle the significant dead and live loads associated with fly systems.

Pipe Batten

Trim Chain

Smoke Pocket

Rope Lock

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Counterweight Arbor

    The counterweight rigging systems are the most common fly systems in performing arts facilities today.

    In a typical counterweight fly system, an arbor (carriage) is employed to balance the weight of the batten and attached loads to be flown above the stage. The arbor, which carries a variable number of metal counterweights, moves up and down vertical tracks alongside an offstage wall. In some lower-capacity fly systems, cable guide wires are used instead of tracks to guide the arbors and limit their horizontal play during vertical travel (movement).