I'm trying to gauge the overall interest in a book aimed at marketing and advertising professions and would love to know the overall market size. Thanks!!

The problem in answering this question is that there is no fixed line that defines "marketing and advertising professions." Millions of small business owners and managers have substantial responsibility for advertising and marketing their businesses. The real question is how large is the "target audience" for your book, and that usually depends on the specific subject.

For example, if your book is about "layout techniques for newspaper advertising," or "managing affiliate marketing programs," then your target audience is relatively narrow, but if your subject is "improving the effectiveness of advertising" or "writing effective call-to-action copy" then perhaps the potential market is larger.

If your book will target just people who are in the "advertising industry" (ad agencies, for example), then you might look to the circulation figures for magazines like Advertising Age or AdWeek.