By means of a mathematical transformation, we introduce a set of reference frames, called superluminal inertial frames, relative to which tachyons in one spatial dimension behave as ordinary particles. One-dimensional processes involving tachyons and photons can be analyzed in the new frames, and the results transformed to the subluminal frames. The mathematical symmetry or duality between subluminal and superluminal frames and particles suggests an extension of the principle of relativity, acco