Wetland function assessment is not only a basic step to understand wetland ecosystems in detail but also an important process as a base of the term, ecosystem service to recognize wetland ecosystems as valuable and useful resources and goods for human being. WET (wetland evaluation technique), EMAP (environmental monitoring assessment program)-wetlands, and HGM (hydrogeomorphic method) were developed as pioneer wetland function assessments in U.S. at the end of 20th-century. RAMs (rapid assessment methods) became a major function assessment tool which is relatively simpler and easier assessment tool at the beginning of 21th-century. After that, the hierarchy of three levels of assessment (landscape assessment, rapid assessment, and intensive assesment) has been prepared and strategically utilized according to the objectives and purposes of function assessments. In South Korea, RAM and HGM were used to assess wetland functions with reforming a couple of items and contents at 2001. And, modified and reformed function assessments have been developed to complement and improve upon the existing RAMs and HGMs. Via the trend analysis on wetland function assessments, some needs which require supplements in terms of function assessment are pointed out: 1) wetland function assessments using useful indicators such as birds are needed with considering our environmental characteristics. 2) optimized wetland function assessments for coastal wetlands are also needed. 3) the network construction and further expansion to lead communications and co-operations between researchers and policy makers is needed in the field of wetland function assessment.