As part of the Arsenic Rule Implementation Research Program, between July 2003 and July 2011, the U.S. Environmental Protection Agency (EPA) conducted 50 full-scale demonstration projects on treatment systems removing arsenic from drinking water in 26 states throughout the U.S. The projects were conducted to evaluate the performance, reliability, and cost of arsenic removal technologies selected for demonstration and to determine their effects on water quality in distribution systems. A key objective was to collect cost and performance data that might be used by small water systems, engineering firms, and state agencies to make informed decisions on selecting appropriate arsenic treatment technologies to achieve the revised arsenic maximum contaminant level (MCL) of 10 micrograms/L. While results from each demonstration are documented in individual technology performance evaluation reports, this report summarizes cost data across all demonstrations grouped by the technology type. For each type of technologies, a brief overview of demonstration sites, demonstration technologies, system designs and configurations, and system operations was provided to assist in understanding relevant cost data. The arsenic demonstration program was divided into three rounds of projects: Round 1 (12 projects), Round 2 (28 projects), and Round 2a (10 projects). Treatment systems selected for demonstration included 28 adsorptive media (AM) systems, 18 iron removal (IR) and coagulation/filtration (CF) systems (including four using IR pretreatment followed by AM), two ion exchange (IX) systems, and one each reverse osmosis (RO), point-of-use (POU) RO, POU AM, and system/process modification. Among the 50 locations, 42 were community water systems (CWS) and eight were non-transient non-community water systems (NTNCWS).