Carbon nanotube possesses one-dimensional tubular structure whose diameter typically ranges from 0.4 to 5 nm. Recently, significant research efforts have been devoted to encapsulate various atoms and molecules into inner space of carbon nanotubes to create novel hybrid one-dimensional materials. In this paper, we review recent studies on carbon nanotubes encapsulating atoms and molecules, where the following topics are discussed in detail:formation of metal atomic wires in carbon nanotubes, structure and dynamics of the atomic wires, chirality control of carbon nanotubes based on fusion reaction in carbon nanotubes and extraction of materials from carbon nanotubes.