  I review the results obtained by long-baseline interferometry at infrared
wavelengths on the innermost regions around young stars. These observations
directly probe the location of the dust and gas in the disks. The
characteristic sizes of these regions found are larger than previously thought.
These results have motivated in part a new class of models of the inner disk
structure. However the precise understanding of the origin of these low
visibilities is still in debate. Mid-infrared observations have probed disk
emission over a larger range of scales revealing mineralogy gradients in the
disk. Recent spectrally resolved observations allow the dust and gas to be
studied separately. The few results shows that the Brackett gamma emission can
find its origin either in a wind or in a magnetosphere but there are no
definitive answers yet. In a certain number of cases, the very high spatial
resolution seems to reveal very close companions. In any case, these results
provide crucial information on the structure and physical properties of disks
surrounding young stars especially as initial conditions for planet formation.
