[en] Theoretical studies were carried out of atomic and molecular phenomena with an emphasis on the properties of highly-ionized systems. Methods were developed for the inclusion of correlation and relativistic effects in the determination of spectral line oscillator strengths and transition probabilities. The process of charge transfer by low energy multiply-charged ions colliding with atomic hydrogen was investigated and cross sections were obtained for many systems. It was pointed out that the favored channels often lead to excited ions which reveal their presence by specific emission lines. A multichannel theory of photodissociation was constructed that incorporates final state interactions. The properties of multiply-ionized molecules were explored and stable systems were identified. Work was carried out on intense field effects, the Berry phase in atomic physics and on processes of chemi-ionization. Plasma density effects on proton-impact excitations of fine-structure levels of hydrogenic ions were calculateed using a static potential model