The industrial importance of SnO2 is in various fields, such as gas sensing, optoelectronics, and energy storage, where it is strongly affected by various unique characteristics of the crystallography. This chapter deeply explores the structural properties of SnO2, focusing on its polymorphs, lattice parameters, and pressure-induced phase transitions. The study deals with mathematical modeling for understanding phase stability, focusing mainly on the Birch–Murnaghan equation of state and correlations of transition pressure. In addition, it analyzes the role of crystallite size and surface energy in determining transition pressures with insights into nanoscale modification. It discusses the variations of lattice parameters for different polymorphs, focusing on the effects of compression on unit cell dimensions. The effect of dopants and defects on crystallographic behavior is also discussed for an understanding of the structural evolution of SnO2. The intent of this chapter thus includes the combination and integration of fundamental theory on crystallography with applications in enabling advancement in SnO2-based technology.