Cosmic rays are a key non-thermal component of galaxies, yet their transport through the interstellar medium remains difficult to model because the ISM is turbulent, magnetized, multi-phase, and often only partially ionized. In this talk, I will discuss how these realistic ISM conditions reshape TeV–PeV cosmic-ray diffusion. I will show that MHD turbulence drives perpendicular superdiffusion through magnetic-field-line wandering, while compressibility, magnetic mirroring, ion–neutral damping, and thermal phase transitions regulate parallel scattering and confinement. These effects are especially important in cold and partially ionized gas, as well as for TeV–PeV cosmic rays propagating through a multi-phase ISM. I will also discuss how these transport mechanisms may help interpret recent LHAASO observations of Galactic PeVatrons and their extended TeV–PeV gamma-ray emission.