Aspects of string field theory

In this dissertation we discuss both formal and practical aspects of string field theory. On the formal side, we investigate string vertices which are essential ingredients of string field theory constrained by the consistency conditions of the formulation. In particular, we find a family of string vertices for open-closed string field theory which manifests hyperbolic structures of Riemann surfaces over which the string worldsheet theory is formulated. On the practical side, we apply superstring field theory based on the Neveu-Schwarz-Ramond formalism to study strings in the Ramond-Ramond flux backgrounds such as pp-wave background and $AdS_3$ background, where we compute the string spectrum perturbatively in the Ramond-Ramond flux. As another application of string field theory, we discuss D-instanton background in type IIB superstring theory and show that the quartic effective potential for the translation zero mode vanishes.