The theremin was invented in 1919 by Russian scientist Lev Termen and is one of the last truly unique instruments, meaning that it doesn't have any relations with already existing instruments. It offers a truly new and fascinating way of making music.
The theremin is basically a cabinet with two antennas . When the instrument is switched on electro magnetic fields will form around both antennas and the musician uses those fields to create different sounds. By waving ones hands in front of the instrument, melodies can be created out of thin air.
How does it work?
The upright right antenna is used for pitch. When ones hand comes closer to the antenna, the pitch will go up and vice versa. The horizontal left antenna is used to control dynamics and articulation. When ones hand is flat on the antenna the instrument is muted, and when it is raised a sound will appear and will become louder as the arm is raised higher and higher. All these hand and arm gestures will be transferred to a speaker so the musician's movements become audible and music can be heard.
Theremin history
The theremin first founds its fame in the 1950's as it was used by Hollywood to create scary sounds in horror and sci-fi movies. This resulted in some beautiful soundtracks featuring the theremin, such as Bernard Herrmann's "The Day The Earth Stood Still" and Miklós Rózsa's "Spellbound". The theremin also founds its way to the concert stages around the world. Thereminists like Lucie Bigelow Rosen and Clara Rockmore toured extensively in the 1930's and 40's. And nowadays composers like Lera Auerbach, Fazil Say, Kalevi Aho, Howard Shore and many others use the theremin in their concert music  
The theremin being a relatively new instrument, new ways of playing and controlling the instrument are invented by today's players and a tradition is being established so that the theremin can claim its rightful place in the world of music.