Does your book really need an index?  The answer is a resounding yes!  See some comments about indexes and indexing from publishing professionals by following these links:

Does Your Book Need an Index? by Mindy Reed.

How to Index Your Book (And Why I’ll Never Do It Again) by Kathleen Fitzpatrick.

Every non-fiction book needs an index: Here’s why.

Do you need to include a Table of contents or Index