Abstract: A discrete valuation of a linear combination of terms is generally greater than or equal to the minimum of the valuations of the terms. A fundamental fact in toric geometry says that if the terms are monomials and the valuation corresponds to a toric boundary divisor, then this inequality will actually be an equality. We call this valuative independence. I'll discuss valuative independence for theta functions on cluster varieties. I'll then explain theta reciprocity, a symmetry property between valuations and theta functions. This is based on joint work with M.-W. Cheung, T. Magee, and G. Muller.