At commencement of the project,The states of New South Wales, Victoria and South Australia had their coastalines mapped as well as areas of southern Queensland and south-west Western Australia. However only broad scale risk mapping was available in the Northern Territory and Tasmania and large gaps also remained elsewhere. To initiate a program of national mapping, a stage 1 atlas of Australian ASS was compiled from various map GIS coverages available from the states and territories. A significant challenge included the major gaps in mapping, various scales of map available, diverse forms and distributions of ASS, different qualities of supporting soil data and differing map legends. The methodology involved assembling and/or linking published ASS, land systems, marine habitat, elevation (DEM), tidal, estuarine, climate, vegetation and remotely sensed data through GIS. The mapping scale of source data ranged from 1:10K aerial photography in South Australia to 1:250K vegetation mapping in Western Australia and Northern Territory, with most east coast mapping being at the 1:100K scale. The national atlas has accommodated scale and map quality differences by incorporating a probability statement. This dataset depicts a national map of available ASS mapping with common legend that includes: (i) High or Low Probability of Occurrence of Acid Sulfate Soils (i.e. > 70% of mapping unit). (ii) Low Probability of Occurrence of Acid Sulfate Soils (i.e. < 70% of mapping unit) (iii) No Known Occurrence of ASS (iv) Not Assessed. Existing state coastal ASS mapping was received and processed to varying degrees to conform to the national map legend. Spatially, all datasets were reprojected from their original projections to geographic GDA94. Classification of state mapping polygons to the national framework was as follows. In the case of South Australia, New South Wales, Queensland and Western Australia it was a matter of directly translating the original state ASS classifications to the national classification. These translations were undertaken by the creators of the state data and other experts within the respective states. Due to the more broad classifications of the original Victorian, Northern Territory and and Tasmanian ASS mapping, polygons for these three states were initially translated to a national classification group (eg Tidal, Non-Tidal) by the data custodians then subsequently differentiated further through intersecting with other layers. These included the 3 second SRTM DEM and North Coast Mangrove mapping GIS datasets. The former being used to differentiate within the Non-Tidal zones and the latter used to differentiate the Tidal zones. Mapping of the Tidal-Zone classes was augmented for all states except South Australia and New South Wales with 1:100K coastal waterways geomorphic habitat mapping. These and other problems were overcome through a national consultative process to develop a user-friendly legend, which provides a national coverage of Australian coastal ASS. The project was released in October 2005 as a web GIS based atlas on (www.asris.gov.au). Based on the national legend framework, individual polygons can be interrogated on the web for their attributes such as probability of occurrence, presence/absence of tidal influence, elevation above sea level, landform element and distinguishing soil/sediment properties (e.g. the predicted depth to and basic nature of the upper ASS layers), vegetation, landforms, age or other characteristics. The map legend accommodates all the coastal ASS known to date, from those that occur as bottom sediments in estuaries to tidal flats, coastal floodplains to sandplains and dunes (some in excess of 10m elevation above sea level) as well as a category for disturbed terrain. The atlas estimates that Australia contains at least 77,249Km2 of land with a high probability of containing ASS, or overall, 94,217Km2 of land with some probability of containing ASS. Of greatest concern is the 943Km2 of high probability ASS that has been profoundly disturbed and potentially acidified. The majority of Australian ASS are of Holocene age, although extensive areas are found beneath sand plains and dunes >10m elevation(5959 Km2 confirmed). The Atlas of Australian coastal acid sulfate soils is a component of the Australian Soil Resource Information System or ASRIS, recently established on the world wide web. At a national scale these products identify the known current extent and severity of the coastal ASS problem using a standardised approach for all jurisdictions and allow for risk assessment in terms of maintenance of existing development and of future development proposals. The authors wish to acknowledge the various state and territory institutions that provided access to their ASS maps. Individuals who supplied data and provided input into developing the structure of the national legend include Mitch Tulau, Glen Atkinson and Greg Chapman ( New South Wales), Brad Degens (Western Australia), Wojciech Grun (Tasmania), Don Malcolm (Queensland), Dave Howe, (Northern Territory), Tim Noyce (South Australia) and Richard McEwan, Austin Brown, Nathan Robinson, (Victoria). The support of Neil McKenzie and David Jacquier of CSIRO Land and Water were critical to the successful establishment of the Atlas as a web-based GIS system on the ASRIS website.