This study concentrates on pair distribution function (PDF) analysis of various related systems under extreme conditions using variable temperatures and pressures. The local structure of BaTiO\(_3\) (BTO) was investigated using x-rays (xPDF) between 0 and 8.78 GPa and x-rays and neutrons (nPDF) between 100 and 500K. Evidence is presented that indicates that the “Comes model” of Ti disorder is too simplistic to describe the local structure of BTO at variable temperature but results from the high pressure xPDF study are inconclusive due to the inability to observe the very weak first Ti-O peak. The ambient structure of related Ba\(_1\)\(_-\)\(_x\)Bi\(_x\)Ti\(_1\)\(_-\)\(_x\)Yb\(_x\)O\(_3\) was also investigated using both nPDF and xPDF between x = 0 and 0.15, with PDFs indicating significant local disorder present on both A and B sites. Cubic ZrMo\(_2\)O\(_7\) undergoes pressure induced amorphisation at ~0.7 GPa and this was investigated up to 11.02 GPa using xPDF which showed an increase in Mo coordination with pressure but no significant change around Zr. Iron undergoes a bcc-hcp phase transition between 10 and 20 GPa and xPDF was used to investigate this phase transition and the local structure of the hcp phase up to 50.07 GPa, but texture in the sample at high pressures hindered analysis.