"The American Society for Indexing, Inc. (ASI) is a national association founded in 1968 to promote excellence in indexing and increase awareness of the value of well-written and well-designed indexes. ASI serves indexers, librarians, abstractors, editors, publishers, database producers, data searchers, product developers, technical writers, academic professionals, researchers and readers, and others concerned with indexing. It is the only professional organization in the United States devoted solely to the advancement of indexing, abstracting and related methods of information retrieval."
An author's perspective on the value of the indexer's work:
From The Chronicle of Higher Education, "My Last Index"