Lots of books have been written about ferrets, ranging from brief
treatments to extensive discussions of behavior and medical issues.
Introductory books, all most owners will ever need, are usually
available in pet stores.  A few of the more popular are

Biology and Diseases of the Ferret, by James G. Fox.  Lea and Febiger,
   Philadelphia (1988).  ISBN 0-8121-1139-7

The Pet Ferret Owner's Manual, by Judith A. Bell, DVM, PhD.
   ISBN 0-9646477-2-9 PB, 0-9646477-1-0 LB.
    Clear, well-written and comprehensive, with lots of color
    photographs.  Dr. Bell is an internationally known expert on
    ferret medicine and care.

A Practical Guide to Ferrets, by Deborah Jeans.  Contact the author at
   Ferrets Inc., P. O. Box 450099, Miami, FL 33245-0099; fax
   305-285-6963.
     "Excellent, easy to read, very thorough and up to date, and
     written with a lot of love and care," says Dr. Susan Brown, DVM.

Ferrets: a Complete Owner's Manual, by Chuck and Fox Morton.  Barron's
   Educational Series, Hauppauge, NY, 1985.  ISBN 0-8120-2976-3
     A relatively short, but well-written guide.  Not as in-depth as
     some, but a very good, friendly introduction to ferrets as pets.

Ferrets in Your Home, by Wendy Winsted.  T.F.H. Publications,
   Inc., Neptune City, NJ, 1990. ISBN 0-86622-988-4
     Longer and more in-depth, but still very readable.  Includes, for
     instance, more information on reproduction and breeding, but also
     more expensive.

For somewhat more in-depth medical and natural history information, Bob
Church recommends

Ferrets, Rabbits and Rodents - Clinical Medicine and Surgery, by Elizabeth
   Hillyer and Katherine Quesenberry (1997)

Wild Mammals of North America, by Chapman and Feldhammer (1989)
     Use the section about mink, perhaps tempered somewhat with the
     black-footed ferret.  Together, they are very similar to the
     polecat, which is the driving force behind our ferrets.

Ethology: the Mechanisms and Evolution of Behavior, by James Gould (1982)