Assessing the threat status of ecosystems is a useful tool for understanding biodiversity loss on Earth. In 2008, the International Union for Conservation of Nature (IUCN) established a working group at the fourth World Conservation Congress to develop quantitative categories and criteria for assessing ecosystem threat status. These categories and criteria were similar to those used to assess extinction risk for species. This working group strove to establish red lists of ecosystems by applying these criteria to ecosystems at local, regional, and global scales. Ecosystem red lists were designed to be complementary to species red lists for use in creating biodiversity conservation policies. The criteria used for assessment were grouped into four classes: short-term decline in distribution or ecological function, historical declines in distribution or ecological function, small current distribution with decline in distribution or ecological function, or very restricted current distribution. In this paper, we illustrate the use of these criteria for assessing ecosystem threat status; we used literature data on the areas of occupancy for four ecosystems in China’s Liaohe Delta in 1988 and 2006 to evaluate the threat status of these four ecosystems. We also discuss challenges that lie ahead for this method of assessment. Measures of ecosystem distribution and area of occupancy should be based on proper spatial scales. Appropriate quantitative methods are also needed to measure changes in ecosystem function. The final proposed assessment protocol will be presented for further discussion at the 2012 World Conservation Congress.