A study of the optical properties and electronic structure of molybdenum is reported in a two-paper experimental and theoretical series. Reflectivity data between 0.5 and 6 eV are presented, and Kramers-Kronig analytical procedures used to determine the optical functions ɛ1(ω) and ɛ2(ω) are discussed. Procedures are discussed for obtaining suitable extrapolations of R(ω) in the ranges ω-->0 and ω-->∞. (ω and ω are the energy extremes of the measured spectral range.) A new method (for metals) is presented for optimizing the extrapolation R(ω) in the range ω-->0. Recently reported sum rules are evaluated to test the inversion procedures.