The content of this last chapter should be regarded merely as whetting the appetite for superstring theory at large. We explore the bare basic structure of spacetime theories as implied by certain models of supersymmetric fundamental strings, with emphasis on bosonic fields and their mutual interactions. Spacetime supersymmetries enter conveniently in determining the spacetime field content, their kinetic terms, and the lowest interaction among them. On the other hand, there are also higher-derivative "topological" terms that are fixed entirely by cancelations of potential gauge and gravitational anomalies combined with various "dualities" that are hallmarks of superstring theories. Starting from the mysterious M-theory in eleven-dimensional spacetime, we derive type IIA and IIB theories in ten dimensions by such dualities, and keep track of "topological" terms. After going through various dimensionally reduced models with the same number of supercharges kept, we close with type I theories and the celebrated Green-Schwarz mechanism.