After an introduction to interferometry, I will first present interferometric H band observations of Betelgeuse obtained with the IOTA instrument. The low spatial frequencies part of the dataset revealed the presence of a likely dusty environment located at 5 stellar radii. Three-telescope interferometry allow to probe the asymmetry of the observed object by measuring a quantity called closure phase. These measurements have been fitted and used together with the visibilities to achieve a parametric imaging of Betelgeuse. I will also show reconstructed images carried out with the MIRA and WISARD routines. To conclude this part, I will compare these data to the predictions from hydro-radiative 3D simulations. In a second part, I will introduce a new infrared adaptive optics assisted multiple-beam instrument for the VLTI infrastructure. GRAVITY, standing for General Relativity Analysis via VLT InterferometrY, will particularly probe space time around SgrA*, the supermassive black hole at the center of our galaxy. It will be able to detect relativistic effects at a few Schwarzschild radii of the center of the black hole thanks to an astrometric accuracy of 10 micro arcseconds.