  In three years of observations since the beginning of nominal science
operations in August 2008, the Large Area Telescope (LAT) on board the Fermi
Gamma Ray Space Telescope has observed high-energy (>20 MeV) \gamma-ray
emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been
detected above 100 MeV and 7 GRBs above ~ 20 MeV. The first Fermi-LAT catalog
of GRBs is a compilation of these detections and provides a systematic study of
high-energy emission from GRBs for the first time. To generate the catalog, we
examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and
processed each of them using the same analysis sequence. Details of the
methodology followed by the LAT collaboration for GRB analysis are provided. We
summarize the temporal and spectral properties of the LAT-detected GRBs. We
also discuss characteristics of LAT-detected emission such as its delayed onset
and longer duration compared to emission detected by the GBM, its power-law
temporal decay at late times, and the fact that it is dominated by a power-law
spectral component that appears in addition to the usual Band model.
