  In this paper, we review the various ways in which an infrared stellar
interferometer can be used to perform direct detection of extrasolar planetary
systems. We first review the techniques based on classical stellar
interferometry, where (complex) visibilities are measured, and then describe
how higher dynamic ranges can be achieved with nulling interferometry. The
application of nulling interferometry to the study of exozodiacal discs and
extrasolar planets is then discussed and illustrated with a few examples.
