tions given in the Appendix) for the e-ph induced superconductivity. The same is expected for e-e induced superconductivity. I will discuss the variation of T$_{c}$ with the variation in the distribution in frequency of the spectral weight of the fluctuations, subject to their integral being held a constant. This includes the discussion of the effects of inelastic scattering in depressing T$_{c}$ (and raising the ratio (Δ /T$_{c}$ )). Important differences between s-wave and finite angular momentum pairing is evident from this analysis. Using this it will be shown that the simplest class of quantum- critical fluctuations (called Gaussian fluctuations here) are bad for T$_{c}$ . In this class the frequency spectrum of the fluctuations is peaked near thermal frequencies. I will review that the form of critical fluctuation spectrum consistent with the normal state experiments in cuprates and the heavy-fermions and quite likely the pnictides does not suffer from this limitation. Armed with this general knowledge, I pass on to the semi-empirical information on vari- ous classes of materials and its understanding based on the above. First superconductivity in transition metals and compounds through e-ph interaction is reviewed, in Sec. III. There are several things to be learnt here because a variety of experiments provide inter-relationships between parameters which determined T$_{c}$ . Simple theoretical ideas have been used to un- derstand such relationships. I argue that this understanding is useful for the e-e problems as well. In preparation for pairing in metals due to e-e interactions, I will review the connection between vertices of Fermi-liquid theory, in particular the Landau parameters and the pairing vertex in Sec. IV. This will be accompanied by empirical information and calculations on the superfluidity of He $^{3}$. I will then discuss superconductivity through other interactions. The discussion will be based both on data, empirical considerations and the theoretical guidance which is available. Superconductivity in Heavy-Fermions, Cuprates, Pnictides and the interesting case of Ba$_{1}$$_{−}$$_{x}$K$_{x}$BiO$_{3}$ , which appears to have electronically induced s − wave pairing, are successively discussed in light of the theoretical discussion. Major unsolved experimental and theoretical issues are highlighted. What limits the T$_{c}$/E$_{f}$ for finite ℓ e-e induced pairing? There is first of all the deleterious effect on T$_{c}$ of the normal self-energy which is principally determined by the coupling constant λ$_{0}$ in the s − wave channel. Generally this is larger than the coupling constant for the pairing self-energy λ$_{ℓ}$ . This is because the important effective interactions are always short-range. 9