The OH molecule can be observed at cosmological distances both in maser emission and in absorption. OH megamasers identify major galaxy mergers and associated circumnuclear starbursts and massive black holes, and they mark the very early stages of binary massive black hole formation. I will review the multi-wavelength foundation required to use OH megamasers as tracers of these phenomena and outline current and future surveys at high redshift. OH absorption lines, on the other hand, can provide precise constraints on the evolution of the fine structure constant over cosmic time. I will outline the motivations, methods, and prospects for this new technique including new line detections, new constraints on the evolution of the fine structure constant, and a new method to identify damped Lyman alpha and molecular absorption systems.