PIPs are now widely used in a number of areas of theoretical/computational chemistry including chemical reactions as indicated above, unimolecular reactions, spectroscopy, the statistical mechanics of water, many-body non-covalent interactions for clusters, guest-host systems, etc. And while a detailed review of this body of work would be worthwhile, that is not done here. The aim here is to present the recent and substantialk advances and PIPs methodology since 2018, when the last review of PIPs appeared. The next section presents a brief review of PIPs and current software to generate them.