Experiments (many at ISIS) using crystallographic methods, total scattering, inelastic neutron scattering and theory have provided a detailed picture of the origin of strong negative thermal expansion (NTE) in ZrW2O8. We have recently produced large samples of SnMo2O8 which appears to be isostructural with this famous NTE materials, yet shows positive thermal expansion and non-reconstructive high temperature phase transitions. The existence of isostructural materials with strong negative and positive thermal expansion offers a possibility of producing true zero-expansion solid solutions. We request 4 days on GEM to understand the structure and dynamics of this fascinating and potentially important material.