 The purpose of this study is to see if recent guidelines proposed by the National Institutes of Health for the diagnosis, staging, and response assessment of people with chronic GVHD can improve our understanding of this complication. We will accomplish our goals by studying a large number of people with chronic GVHD over several years using information collected from health care providers, patients, laboratory studies and diagnostic tests. Several transplant centers in the United States are collaborating on this project. 