  We introduce and discuss the concept of modular entanglement. This is the
entanglement that is established between the end points of modular systems
composed by sets of interacting moduli of arbitrarily fixed size. We show that
end-to-end modular entanglement scales in the thermodynamic limit and rapidly
saturates with the number of constituent moduli. We clarify the mechanisms
underlying the onset of entanglement between distant and non-interacting
quantum systems and its optimization for applications to quantum repeaters and
entanglement distribution and sharing.
