Clusters are aggregates of atoms/molecules, which exhibit completely different properties from their constituent atoms/molecules. They show drastic variation in chemical/physical properties as a result of addition/deletion of single atoms/molecules. Thus, studies have been focused to develop cluster assembled materials for various applications by varying numbers of constituent atoms/molecules within a cluster. In the book chapter, synthesis of gas-phase free clusters and stabilisation of these free clusters by different methods has been discussed. To understand the property of free and supported clusters, various sophisticated spectroscopic and microscopic techniques have been described. Size-selected free cluster and ligand-protected clusters are successfully utilised in various fields, which include physics, chemistry, biology, etc. In the field of chemistry, cluster materials have been judiciously applied as catalyst in different important reactions, such as CO oxidation and hydrogenation reaction. In addition, ligand-protected clusters are also used as bio-sensor and as bio-imaging agent. Moreover, clusters interact with intense laser pulses lead to generation of energetic multiply charged cations and electrons, which have potential for development of table-top accelerators. Thus, clusters and cluster assembled materials have emerged as a new class of material with multi-facet applications in science and technology.