Binary star research is one of the oldest fields of astronomy, and yet also one of the most active. In fact, the majority of stars happens to be part of a binary or multiple system, and consequently binary star research covers most areas of stellar astronomy: from the youngest objects to the most evolved ones, from the least to the most massive. From the observational point of view, binary star research has always been strongly linked to the techniques available to push the limits of angular resolution and sensitivity. Significant steps ahead have occurred with the introduction of speckle interferometry, of lunar occultations, of adaptive optics. It is easy to predict that, thanks to its long and flexible baselines and to the large photon- gathering power, the VLTI will create the opportunity for another step ahead in this field. We investigate the potential applications of VLTI for binary star research, in particular with respect to studies of (1) T Tauri stars and associated star-formation mechanisms, and (3) dynamical mass determinations of low-mass stars. We present some recent results obtained by speckle interferometry and lunar occultations in these two areas, and discuss the follow-up studies which will become feasible with the VLTI.