The AMBER instrument installed at the Very Large Telescope (VLT) combines the beams from three telescopes to produce spectrally dispersed interference fringes with milli-arcsecond angular scales in the near infrared. Three years after installation, first scientific observations have been carried out mostly during the Science Demonstration Time and the Guaranteed Time. The first science has mainly focused on the environment of various types of stars. Because AMBER has dramatically increased the number of measures per baseline, this instrument brings strong constraints on morphology and models. AMBER is one of the two science instruments of the Very Large Telescope Interferometer (VLTI) described in Petrov et al. (2007). AMBER is an interferometric beam combiner for the VLTI working in the near-infrared J-, H-, and K-bands and able to simultaneously mix three beams coming from three identical telescopes. AMBER interferograms are spectrally dispersed with a resolution of about 35, 1500, or 12 000. Therefore the instrument can measure visibilities and a closure phase in a few hundred different spectral channels. The spectral coverage, the spectral resolution, and the better sensitivity compared to small-aperture interferometers give access to many new astrophysical fields that we describe in this paper.