Nanoclusters (NCs) are aggregates of a countable number of particles which can exist in both condensed and gas phases. Gas phase unprotected clusters known as ‘naked clusters’ are ensembles of atoms or molecules that do not have a stabilizing ligand shell. These gas phase naked clusters bridge the gap between the molecules and materials by allowing the molecular level studies of their gas phase properties in the absence of ligands and solvent medium. Typically, these clusters are extremely reactive under ambient conditions due to the absence of protecting ligands and cannot be stored in their free state. In a typical experiment, naked clusters are prepared in a vacuum or under an inert atmosphere where their properties are investigated and their characterization is performed. The methods of preparation of a variety of naked clusters and various ionization and detection techniques have been discussed in this chapter. Further, their gas phase reactivity, catalysis, various characterization techniques, clusters supported on solids are also discussed in detail.