There are many ways of determining a first edition. The link below tells some.

Here is a link that might be useful: ID a first edition

ALL books have a first edition ... and most of the older ones were not marked as such. The second edition is usually identified as being the second.

It's only when a book with a small first edition becomes popular that the value rises ... because of rarity.

Go to http://used.addall.com/ and start looking them up by author and title.

Pay close attention to condition, including dustjackets if any - I have a book I bought for $75 that in better condition sells for thousands.

Here is a link that might be useful: Used and antique book search

Actually most books have only a first edition!

Lindac is correct, especially with more current books. I have a large collection of first edition books, some found in Half Priced book stores. Sometimes a popular book that is first edition in hard back may go into paper back. Some authors had manuscripts that were never published until published by an heir. Hemingway falls into this catagory in a few instances. Mary Hemingway did this with "Islands in the Stream."

Thanks, everyone. This is extremely helpful info. I doubt that my books are worth much because of condition. It seems condition is key. These are all intact but many are w/o dust jackets, pages yellowed, and somewhat dirty. They were kept in sealed boxes but the house had been heated with coal and things are grimy in the attic and basement where the boxes hadn't been touched for probably 50 years.