Thanks to the development of long baseline facilities, near infraredinterferometry is becoming an important tool to study the innermostregions of circumstellar proto-planetary disks around close-by pre-mainsequence stars. Providing a milli arcsecond spatial resolution and spectroscopic capabilities, the existing interferometers can, for thefirst time, spatially resolve and separate the gas and dust emissionarising form the disk regions where planets are supposed to form,namely inside few Astronomical Units from the central star. Theobservational limitations and the complexity of the resulting datarequire however to perform the data analysis in the Fourier space bythe comparison with theoretical disk models. To this purpose a numberof self consistent radiative transfer models have been recentlydeveloped. In this chapter I will first review some of the most recentobservational and theoretical results and then, discuss some importantfuture challenges.