“Nearsightedness of Electronic Matter” (NEM) is a general principle which can be viewed as underlying concepts such as the chemical bond and transferability. Very qualitatively speaking, it describes the fact that: the magnitude of the effect a perturbing potential w(r′), no matter how strong and extended, on a physical property like the density n(r) at the point r, is limited, │Δ n(r)│ ≤ Δ n max (r, R) provided that │r′ - r│ exceeds a given distance R for all r′, while the chemical potential is kept fixed; and that Δ n max (r, R) tends to zero with R in a manner characteristic of the unperturbed system. A quantitative formulation and several illustrations will be presented.