In transition metal perovskite oxides ABO3, it is well established that there is a strong interplay between BO6 octahedra tilting and material property. While the hydrostatic pressure dependence of this tilting has been much explored in this class of materials, comparatively little is known about it in the layered Ruddlesden-Popper (RP) variant. Due to the recently reported high-pressure unconventional superconductivity (SC) in the n = 2 family member La3Ni2O7, [1] this is a point that deserves significant further investigation. Predating this discovery, the n = 2 RPs have attracted our attention in light of the “hybrid” improper ferroelectricity some compositions exhibit that is tied to the simultaneous occurrence of structural distortions characterised by both BO6 rotations perpendicular to, and tilting away from, the layering axis. [2] We have gone on to show how the temperature dependent evolution of these tilting and rotation “order parameters” behave in a distinct way to the situation observed in perovskites.[3] Motivated by this we have focused on investigating the pressure dependence of these order parameters in layered perovskites. Here I will present results [4-6] from high pressure diamond anvil cell X-ray and Paris-Edinburgh neutron diffraction studies, that detail the varying evolution of octahedral tilting and rotations in n = 1 and n = 2 Ruddlesden-Poppers that have relevance for superconductivity, negative thermal expansion, hybrid improper ferroelectricity and the Rashba spin-splitting effect. References: [1] Signatures of superconductivity near 80 K in a nickelate under high pressure. Sun, H. et al. Nature 621 (2023) 493. [2]Negative Thermal Expansion in Hybrid Improper Ferroelectric Ruddlesden-Popper Perovskites by Symmetry Trapping. Mark S. Senn, et al. Phys. Rev. Lett. 114 (2015), 035701. [3] From first- to second-order phase transitions in hybrid improper ferroelectrics through entropy stabilization. Fernando Pomiro, et al. Phys. Rev. B 102 (2020), 014101. [4]Pressure-dependent phase transitions in hybrid improper ferroelectric Ruddlesden-Popper oxides. Gabriel Clarke, et al. Phys. Rev. B 109 (2024), 094107. [5]The varying temperature- and pressure-induced phase transition pathways in hybrid improper ferroelectric Sr3Sn2O7. Evie Ladbrook, Jeremiah P. Tidey, Fei-Ting Huang, Sang-Wook Cheong, Dominik Daisenberger, Mark R. Warren, and Mark S. Senn. Acta Cryst. B 81 (2025) (https://doi.org/10.1107/S2052520625002306) [6]Pressure induced enhancement of polar distortions in a metal, and implications on the Rashba spin-splitting. Evie Ladbrook, Urmimala Dey, Nicholas C Bristowe, Robin S Perry, Dominik Daisenberger, Mark R Warren, Mark S Senn. Accepted Phys. Rev. B Phys. Rev. B 111 (2025), 205110.