Although the superstring possesses world sheet supersymmetry, it does not possess space-time supersymmetry. However, a potential problem of tachyonic ground states is avoided by applying a projection to the states of the theory, and after this projection has been applied a ten-dimensional space-time supersymmetric theory is obtained. In this chapter, the authors concentrate on the closed superstring which, by providing the right movers for the heterotic string, has been the basis for all phenomenologically promising super-string theories to date. The superstring degrees of freedom in the covariant gauge not only obey the wave equations but are also subject to the constraint equations. The super-Virasoro algebra for the right movers with Neveu–Schwarz boundary conditions for the right-mover fermionic degrees of freedom can be derived from the explicit expressions using the commutators of the bosonic oscillators and the anti-commutators of the fermionic oscillators.