  This chapter discusses the use and possibilities of optical and infrared
interferometry to study star formation. The chapter starts with a brief
overview of the star formation process and highlights the open questions from
an observational point of view. These are found at the smallest scales, as this
is, inevitably, where all the action such as accretion and outflows, occurs. We
then use basic astrophysical concepts to assess which scales and conditions can
be probed with existing interferometric set-ups for which we use the ESO/VLTI
instrument suite as example. We will concentrate on the more massive stars
observed at high resolution with continuum interferometry. Throughout, some of
the most recent interferometric results are used as examples of the various
processes discussed.
