The recently discovered in-plane optical anisotropy of (001)-grown quantum wells offers a new theoretical and experimental insight into the electronic properties of semiconductor interfaces. We first discuss the coupling of X and Y valence bands due to the breakdown of rotoinversion symmetry at a semiconductor heterointerface, with special attention to its dependence on effective parameters such as the valence band offset. The intracell localization of Bloch functions is explained from simple theoretical arguments and evaluated numerically from a pseudopotential microscopic model. The role of envelope functions is then considered, and we discuss the specific case of no-common atom interfaces. Experimental results and applications to interface characterization are presented, and the potential of the "quantum confined Pockels effect" for device applications is finally discussed.