In this book we discuss the photoabsorption processesof several closed shell systems, including atoms thatare trapped inside a fullerene molecule. Energylevels and wavefunctions are studied using Dirac-Fockmethod and we employed Relativistic Random PhaseApproximation (RRPA) and Relativistic MultichannelQuantum Defect Theory (RMQDT) to calculate thephotoionization parameters. Autoionizationresonances in Kr, Xe and Cd atoms and the Si2+ ionhave been presented and these results are discussedin the context of some very recent and sophisticatedexperimental results. The effect of confinement has beenmodeled by a spherical annular attractive shellpotential as has been done in an earliernon-relativistic study. Simultaneous effects ofconfinement, relativistic interactions andcorrelation on energy levels, wavefunctions andphotoionization parameters have been discussed indetail. This book is particularly useful for thosewho are working in atomic and molecular physics andrelated fields. This work has been done while Dr.Hari R. Varma worked as a PH.D. student at I.I.T.Madras under the guidance of Dr. P. C. Deshmukh.