A selection is presented of problems in the physics and chemistry of vacuum systems and devices which has attracted considerable research during the past 50 years. These include examples where the limiting gas sources are water vapor, hydrogen, or helium. Also considered are self-sustained crossed-field discharges and the interaction of molecules, electrons, ions, and photons with the "technical" surfaces found in most vacuum systems.@footnote 1@ @FootnoteText@ This manuscript was prepared by J.P.Hobson shortly before his death.