The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the universe using the baryon acoustic oscillations technique. The spectra of 35 million galaxies and quasars over 14,000 square degrees will be measured during a 5-year survey. A new prime focus corrector for the Mayall telescope at Kitt Peak National Observatory will deliver light to 5,000 individually targeted fiber-fed robotic positioners. The fibers in turn feed ten broadband multi-object spectrographs. This talk will give an overview of the DESI project and then describe several unique instrument and survey challenges. I will highlight the ProtoDESI experiment, an on-sky technology demonstration with the goal to reduce technical risks associated with aligning optical fibers with targets using robotic fiber positioners and maintaining the stability required to operate DESI. The ProtoDESI prime focus instrument, which was installed and commissioned on the 4-m Mayall telescope from Aug. 14 to Sep. 30, 2016, consisted of three fiber positioners, illuminated fiducials, and a guide camera. ProtoDESI was successful in acquiring targets with the robotically positioned fibers and demonstrated that the DESI guiding requirements can be met. Additionally, I will report progress on a predictive sky background model for DESI, built on the spectra from the 4-year Baryon Acoustic Oscillation Spectroscopic Survey (BOSS). This dataset consists of ~1 million unique sky spectra covering 360 - 1040 nm collected in a variety of observational conditions. This detailed model will be integrated into a dynamic exposure time calculator for DESI, which will ensure data quality uniformity and increase survey efficiency.
