The energies of spin singlet and triplet bound electron pairs are reckoned for electrons interacting through the Coulomb interaction, while sitting on neigbouring lattice sites. It is concluded that triplet pairs are unlikely to be observed due to screening. The interplay of inter-electron couplings of different spatial range is investigated. High-pressure induced superconductivity is analysed and qualitative agreement is achieved with observed results by working out the dependence of the critical temperature on the microscopic parameters, characterising the electron motion. This approach can be applied to other kinds of inter-electron interactions.

A procedure, dedicated to superconductivity, is extended to study the properties of interacting electrons in normal metals in the thermodynamic limit. Each independent-electron band is shown to split into two correlated-electron bands. Excellent agreement is achieved with Bethe's wave-function for the one-dimensional Hubbard model. The groundstate energy, reckoned for the two-dimensional Hubbard Hamiltonian, is found to be lower than values, obtained thanks to the numerical methods. This analysis applies for any spatial dimension and temperature.

A new picture of the Josephson effect is devised. The radio-frequency (RF) signal, observed in a Josephson junction, is shown to stem from bound electrons, tunneling periodically through the insulating film. This holds also for the microwave mediated tunneling. The Josephson effect is found to be conditioned by the same prerequisite worked out previously for persistent currents, thermal equilibrium and occurence of superconductivity. The observed negative resistance behaviour is shown to originate from the interplay between the normal and superconducting currents.

A classical model is presented for persistent currents in superconductors. Their existence is argued to be warranted because their decay would violate the second law of thermodynamics. This conclusion is achieved by analyzing comparatively Ohm's law and the Joule effect in normal metals and superconducting materials. Whereas Ohm's law applies in identical terms in both cases, the Joule effect is shown to cause the temperature of a superconducting sample to \textit{decrease}. An experiment is proposed to check the validity of this work in superconductors of both types I and II.

By taking advantage of a stability criterion established recently, the critical temperature T_c is reckoned with help of the microscopic parameters, characterising the normal and superconducting electrons, namely the independent-electron band structure and a repulsive two-electron force. The emphasis is laid on the sharp T_c dependence upon electron concentration and inter-electron coupling, which might offer a practical route toward higher T_c values and help to understand why high-T_c compounds exhibit such remarkable properties.

The properties of the current-induced Hall effect are analysed, for which the static magnetic field, supplied by an external source in the traditional experiment, is created by the current itself. The special experimental setup, needed for its observation, is described. It is shown how, combined with the skin effect, it could give access to the concentration of conduction electrons in superconductors. Besides this experiment might permit to dodge shortcomings, ensueing from the Meissner effect and limiting severely the sensitivity of the conventional Hall voltage measurement.

The scattering eigenstates of any Hamiltonian of electrons, coupled through a two-body force and moving on a one-dimensional lattice, are shown to be Bethe's wave-functions. The energy of the groundstate is compared with values, obtained previously for the Hubbard Hamiltonian by means of Bethe's wave-function and within the framework of the correlated Fermi gas. The same analysis is applied to electrons, interacting on neighbouring sites. The significance of those various groundstates is assessed with help of thermodynamics.