Excessive inflow and infiltration during wet weather periods into capacityconstrained sewer systems cause sanitary sewer overflows (SSOs). The two major components of wet weather flow are inflow and infiltration, and arc the main factors found in sanitary sewer evaluation studies (SSES) or inflow/ infiltration (III) studies. Control and reduction of inflow and infiltration directly relates to effective controls for SSOs.The interaction and relative proportions of inflow and infiltration determine the extent, effectiveness and cost of control measures. Usually, control of direct inflow is the first source pursued, with the infiltration component either lumped into part of the inflow as an immediate response, or neglected because of the dominance of peak flow rates induced by inflow. The peak flow rate, as compared to sustained elevated flows from infiltration, is usually the sought-after result in SSES or III studies. Successful and accurate estimates of both rainfall-derived inflow and sustained flmvs from rainfall-derived infiltration are therefore the prime determinants ofthe effectiveness and cost of the controls.The objective of this chapter is to summarize and provide some critique of C01l\i1\0\'\ 't'\0\V -pm)ect\on met\1odo\ogies, \)articu\arly methods that\)red\ct rainfallderived inflo~v and infiltration or rainfall-derived inflow/ infiltration (RDH). A summary ofthe most common methodologies is included. Space limitation precludes site by site comparisons of each technique, even if project objectives (and funding) allowed such comparisons to be made.