This chapter focuses on the multiyear journey taken to determine the structure, in which >150 constructs were purified and subjected to crystallization screening, and thousands of crystals were tested for diffraction. Co-crystallization or soaking experiments showed that these residues comprise binding sites for Ca2+, Ba2+, and Gd3+ in both Orai and TRPV6. Structurally, TRPV5 and TRPV6 share ~75% sequence identity with each other and are ~25% identical to the founding member of the TRPV subfamily TRPV1. While TRPV6 and Orai differ completely in sequence, fold, and oligomeric state, close comparison of their structures reveals similarities that underlie resemblances in their biophysical properties. Early mutagenesis studies of TRPV6 and Orai highlighted a single aspartate or glutamate residue as determinants of their permeation properties, and it was proposed for both channels that high Ca2+ selectivity is conferred by the coordination of Ca2+ by these side chains.