In this talk we introduce and discuss the concept of physical links.
This idea allows to substantiate the type, degree and size of mutual entanglement that spontaneously arises in systems were many fluctuating filaments share the same region in space.
We show that this method is general, straightforward to implement, and hence
applicable to diverse physical situations such as linked ring polymers at equilibrium, mechanically stretched links and concentrated solutions of linear chains.
An extension of this approach to other systems such as reconnection events and topological simplification in dissipative fields and defect lines will be discussed as well.

Work in collaboration with M. Caraglio and C. Micheletti