This chapter describes how bowed string instruments such as the violin, viola, cello, and bass can be modeled using equations that describe their most significant physical attributes. It discusses the structure of a bowed string instrument and presents a description of the development of the research on vibrating strings. In 1909, the Indian physicist C. V. Raman extended Herman Von Helmholtz’s work and showed that there are many other possible periodic solutions for the bowed string. Musical instruments such as the clarinet, the flute, and the bowed string can be defined as self-sustained, which means that sound is produced as long as a source of energy is provided to the instrument. The excitation mechanism in a bowed string instrument is given by friction, the tangential force between objects in contact. For bowed string instruments, the excitation is the bow–string interaction, while the resonator is the vibrating string connected to the body of the instrument.