  We present SPIFFI, the integral field spectrometer for the VLT. This
instrument allows simultaneous observation of infrared spectra in more than
1000 image points of a two dimensional field. With its set of four gratings and
a pixel scale that can be varied by a factor of ten, SPIFFI provides high
flexibility, and at the same time offers the unique possibility of diffraction
limited imaging spectroscopy at an 8m-class telescope, when fed by the adaptive
optics system MACAO. We outline the scientific drivers for building such an
instrument, the concept of image slicing, the optical design, and the
implementation of SPIFFI.
