The papers in this volume were originally presented at the 18th European Junior Scientists Workshop (EJSW), Portugal, on 8-11 November 2003 and at the 1st Asian Junior Scientists Workshop (AJSW), Malaysia, on 7-10 February 2004. The workshops were organised by the SS&PWG (Sewer Systems and Processes Working Group) of the IWA/IAHR Joint Committee on Urban Drainage. The two separate workshops were convened under the general themes of "e;Sewer Processes, Networks and Urban Drainage"e; and specific topics covered included integrated modelling of urban water systems; modelling of pollutant loads; calibration of models; bed-load transport; sewer pipe roughness; advection in sewers; anoxic processes; infiltration and exfiltration; runoff source control; pollutant loads; ventilation and oxygen uptake. From the 37 full papers presented at the two workshops, 16 papers have been selected by independent reviewers from the SS&PWG for publication in Sewer Networks and Processes within Urban Water Systems. They reflect rather well the variety of topics presented during both workshops, and bring the high-quality work of these junior authors to the wider audience it merits.