Abstract: A rebar cage assembly system, a modular jig system and method for forming a rebar cage are disclosed. The rebar cage assembly system includes a modular jig for forming a rebar cage. The modular jig includes a fixture base, and a plurality of jig subcomponents. The jig subcomponents each having a jig attachment feature and a rebar retention feature. The rebar retention feature is configured to detachably receive rebar segments. The plurality of jig subcomponents are customizably arrangeable on the fixture base to form a modular jig to cooperatively position rebar segments in the rebar retention features. The rebar cage assembly system further includes a robotic system having a first robot and second robot and a plurality of rebar segments. The first robot is arranged and disposed to independently retrieve and position jig subcomponents and rebar segments. The second robot is arranged and disposed to join rebar segments to form a rebar cage.