The Regional Commission for Fisheries (RECOFI) Regional Technical Workshop on Sustainable Marine Cage Aquaculture Development, held from 25 to 26 January 2009 in Muscat, Sultanate of Oman, was organized following the endorsement of the biannual work plan of the Working Group on Aquaculture (WGA) by the Commission at its fourth session (Jeddah, Kingdom of Saudi Arabia, 7-9 May 2007). The activity was endorsed in view of the growing importance and interest of this aquaculture sub-sector across the region. The workshop focus was on environmental impact assessment and monitoring, and aquaculture licensing for marine aquaculture cage systems. It also aimed at identifying constraints and shortcomings that needed to be dealt with to support the development of the cage industry and facilitate investments from the private sector. The document contains a set of suggestions and recommendations made by the experts with regard to technical and policy requirements needed to support the growth of the aquaculture sector as a whole and more specifically cage fish farming. RECOFI members have been encouraging cage aquaculture over the years, however, the current level of development varies considerably among the countries and, in general, cage aquaculture can only be considered an economic activity in its infant stages of development. The major constraints identified in the establishment of fish cages, particularly along the northwestern shores of the Gulf, have been the limited availability of suitable farming sites characterized by shallow waters, highly fluctuating salinity and temperature levels and inadequate sea currents. Other limitations included price competition from wild-caught fish, inadequate farming technologies for the region and the limited availability of endemic candidate species of commercial importance suitable for cage aquaculture. The report also contains three review documents on marine cage aquaculture in the region, regulation of Norwegian net-cage fish farming, and a review on cage aquaculture licensing procedures prepared as background discussion papers for the workshop. With specific regard to environmental impact assessment (EIA), the discussions held at the workshop clearly indicate that there is a need for the region and individual Commission members to develop an ad hoc EIA format based on the conditions of the local marine environment as this would determine the level of detail and elements needed to complete a meaningful and useful EIA study. The experts also agreed on the importance to establish regional Environmental Quality Standards (EQS) for fish farm sites in order to set the limits for maximum permissible impact on the area exploited by the cage farming industry and assist in establishing monitoring programmes. With regard to cage aquaculture licensing, the experts acknowledged that a clear licence system is required for exercising legal and administrative control over aquaculture operations as it confers different rights and obligations, and allows public control with regard to environmental protection and the economic sustainability of the farming practices. Furthermore, it was noted that the legislation involved and process in aquaculture licensing should be transparent, readily available and include information on processing time, payable fees, etc. A proposed cage aquaculture licence procedure was discussed and proposed at the workshop based on the format developed and adopted by the Sultanate of Oman. Other matters discussed at the workshop included the occurrence of hazardous algal blooms in the Gulf and its effects on fish farming and the possibility of establishing a regional fish cage farm for demonstration, research and training purposes.