Zeolites, with their crystalline microporous structure, are cordial hosts to a wide variety of guests. Traditional absorption techniques, as well as X-ray diffraction and spectroscopic techniques, have contributed to a better understanding of the nature of the host materials’ characteristic cavities, cages and channels. The same techniques, coupled with powerful computational methods, have given new insights into the interactions of guest molecules with their hosts. In turn, this has led to new developments in the direction of structure during zeolite synthesis as well as potentially new applications of guest-host materials. The chapters in this text describe modern research in this field, detailing some of the studies on structure direction in synthesis, characterization techniques, computational aspects, co-ordination and organometallic chemistry, photochemistry, and electronic and optical materials.