Irreversible adsorption/deposition processes are defined as processes in which, once adsorbed, the particles can neither desorb from nor diffuse along the surface. These processes are commonly encountered when macromolecules or colloidal particles deposit on solid surfaces. This article presents a general and unified picture of these processes based mainly on experimental, simulation, and theoretical results accumulated by the authors over recent years. We describe first the influence of surface exclusion effects on the adsorption process under negligible influence of gravity. Essential results relative to the random sequential adsorption (RSA) model are given, The influence of particle diffusion and hydrodynamic interactions during the adsorption process in the deposition zone near the deposition plane on the structure of the assembly of deposited particles and on the adsorption kinetics are analyzed. It is shown that hydrodynamic interactions have the tendency to randomize the position of the particles over the available surface and thus to render the adsorption process RSA-like. Model predictions are confirmed by experimental data. For the deposition of larger particles gravity plays an important role, and the deposition process is characterized by a dimensionless particle radius R* The case of an infinite value of R* is first discussed and the ballistic deposition (BD) model is described. The deposition processes characterized by R* values ranging from 0.6 to 3.3 are then analyzed. For such R* values one observes a smooth transition from the RSA to the ED behavior when R* is increased.