Morphology and Physical Structure of the Interstellar Medium

The morphology of the interstellar medium (ISM) is dependent on the wavelength at which observations are made. Morphologies at different wavelengths reveal interstellar gas components in different physical conditions, thus allow us to probe the physical structure of the ISM. The global structure of the ISM is determined by the gravitational effects of the host galaxy itself and the environment. On scales from a few parsecs to 103 parsecs, the physical structure of the ISM is largely determined by the energy feedback from massive stars. Interactions between massive stars and the ISM not only shape the ISM but also produce the multiple phases of the ISM. Multi-wavelength observations are needed to study the structure and evolution of a multi-phase ISM. The ISM of the Large Magellanic Cloud (LMC) is used to illustrate the environmental effects and the energy feedback from massive stars. The energy feedback is more complex than any recipe can describe.