Thanks to the development of long baseline facilities, near infrared interferometry is becoming an important tool to study the innermost regions of circumstellar proto-planetary disks around close-by pre-main sequence stars. Providing a milli arcsecond spatial resolution and spectroscopic capabilities, the existing interferometers can, for the first time, spatially resolve and separate the gas and dust emission arising form the disk regions where planets are supposed to form, namely inside few Astronomical Units from the central star. The observational limitations and the complexity of the resulting data require however to perform the data analysis in the Fourier space by the comparison with theoretical disk models. To this purpose a number of self consistent radiative transfer models have been recently developed. In this chapter I will first review some of the most recent observational and theoretical results and then, discuss some important future challenges.