The Dark Energy Spectroscopic Instrument (DESI) is installed on the Mayall 4-meter telescope on Kitt Peak, Arizona. It is nearly prepared to undertake a survey of 35 million galaxies with which it will measure the expansion history of the universe using Baryon Acoustic Oscillations. DESI is a very complex instrument. This talk will give a brief overview of the individual systems that make up DESI including the corrector, the focal plane system, the fiber system, the spectrographs and the software orchestrating them together. Included will be some results regarding their performance as installed.