F. The case of Ba$_{1}$$_{−}$$_{x}$K$_{x}$BiO$_{3}$ . E. Superconductivity in the Pnictides. I. INTRODUCTION A. Scope of this Overview Appendix. There are two distinct aspects to the theory of superconductivity [1] based on the Cooper- pair instability of the normal state of metals. The first is the theory for the kinetic energy and for the interaction vertices of electrons as a function of their momenta, spin and energy. The second is the solution of the model specified by the first aspect to understand and to calculate various properties of the superconducting state. In this overview, only the two simplest properties of the superconducting state are considered: the symmetry of the superconducting state and the transition temperature T$_{c}$ . They are the simplest properties since they are (in most cases) provided by the linearized version of the theory. I will discuss both the well understood problem of pairing vertices in the s-wave symmetry and transition temperatures due to electron-phonon interactions (e-ph) as well as the difficult and continuing problem of pairing due to electron-electron (e-e) interactions themselves in lower symmetries. The point of view taken here is that for both e-ph and e-e interactions, the second aspect, for every realized superconductor is solved by the Eliashberg extension [2] of the BCS theory to include the retarded nature of the effective interactions. The validity of this theory rests on the smallness of the parameter λω$_{c}$/W , where λ is a dimensionless coupling constant, ω$_{c}$ is the characteristic high frequency cut-off of the interactions and W is the unrenormalized electronic bandwidth. This parameter is well known to be small enough for the e-ph problem. I will argue that for every known case of superconductivity through e-e interactions as well, this parameter is small enough for the validity of the theory if not for accurate quantitative calculations. This leaves the first part of the problem, which is essentially the problem about the nor- mal state of the metal. The spin and momentum dependence of the interaction vertices can be projected onto the irreducible representations of the lattice. These together with 4