An understanding and ability to predict the transport and deposition of colloids in porous media requires knowledge of processes and interactions that occur at different spatial and temporal scales. The flow field can be solved and mass transfer processes can be quantified at the collector-scale. Here the potential for colloid attachment in the presence of hydrodynamic forces is determined from a balance of applied (hydrodynamics) and resisting (DLVO) torques. Processes of colloid mass transfer and retention can also be calculated at the pore-scale (ensemble of collectors). Differences in collector- and pore-scale studies occur as a result of the presence of small pore spaces that are associated with multiple interfaces and zones of relative flow stagnation. Illustrative examples of colloid retention processes in the smallest regions of the pore space (straining locations) will be presented from micromodel studies and pore-scale colloid transport simulations. Colloid deposition behaviour at the column-scale has frequently been reported to be non-exponential with distance under unfavourable attachment conditions. Profile shape has been demonstrated to be strongly dependent on the colloid size, pore structure, colloid concentration, hydrodynamics, and solution chemistry. To adequately simulate non-exponential deposition profiles, processes related to variability of the pore structure and flow field, surface charge heterogeneity of colloids and porous media, and/or colloid-colloid interactions need to be considered. Various deterministic and stochastic modeling approaches to quantify non-exponential deposition profiles and to test hypothesis with regard to colloid retention will be summarized.