This Proceedings, ""Pipelines 2005: Optimizing Design, Operations, and Maintenance"", contains over 90 papers presented at the Pipelines 2005 conferences held in Houston, Texas from August 21-24, 2005. These papers cover a wide range of topics related to the advancement of water, wastewater, oil, and gas pipelines. Public agencies and private companies are challenged with the task of replacing, rehabilitating, and expanding their pipeline infrastructure to maintain services and supply lines without interruption. Continued advances in pipeline materials, controls, and non-destructive testing support the growth of pipeline network in these communities. This Proceedings is an effective means of sharing the advances in pipeline design, construction, and maintenance among practitioners, researchers, and designers.