A table of contents lists chapter and section titles of a piece, and an index lists different topics discussed within the piece. If searching the book or paper by topic, an index is more helpful than a table of contents.
A table of contents usually appears at the beginning of a book or paper, while the index appears at the end. Also, the table of contents is organized sequentially, showing the reader in what order the chapters and headings appear. The index is usually organized alphabetically, making it easier to find topics. A table of contents is a simple, general outline of the piece, whereas an index is a more detailed inventory of its contents.