This book discusses the fundamentals of string theory. "Strings" were hypothesized to replace the concept of particles being like 'point-mass' objects. Strings are proposed to have various vibrational states. These different vibrational states are seen as particles that have the properties of the four fundamental forces. These fundamental forces are the weak nuclear force, the strong nuclear force, the electromagnetic force and the gravitational force. The ultimate goal of modeling a theory of everything is to use "strings" to accurately represent all four known forces. Grand unification theory has unified all the forces except gravity. String theory is thought to be the next step in quantum gravity theory in order to unite all the known forces into one model.This book is designed to be a reference and provide an overview of the topic and give the reader a structured knowledge to familiarize yourself with the topic at the most affordable price possible.The accuracy and knowledge is of an international viewpoint as the edited articles represent the inputs of many knowledgeable individuals and some of the most current knowledge on the topic, based on the date of publication.