Experimental and theoretical studies of collision and photoionization/ photofragmentation processes involving atoms and molecules, in one form or another, are commonly used in the investigations on a large number of atomic and molecular processes. This is on account of the fact that the collision and photoionization processes are related to each other by the time-reversal symmetry and complement each other. The problems investigated in this book were selected to provide acquaintance - however modest - with both experimental and theoretical techniques employed in both collision and photoionization/ photofragmentation phenomena. Toward this goal, the following three problems have been investigated: 1. Distorted-wave Born approximation studies of (e,2e) collisions. 2. Relativistic many-body correlation studies of spin-orbit interaction activated inter-channel coupling effects in atomic photoionization. 3. Momentum resolved spectrometry-based experimental studies, using INDUS-1 synchrotron radiation source, on the photofragmentation of (a) sulphur hexafluoride and (b) carbon dioxide and theoretical analysis of the fragmentation dynamics of triply ionized carbon dioxide.