What is it for, and where did it come from?
W. H. Smith, who was the largest single book retailer in Great Britain, became computerized and wanted a standard numbering system for all the books it carried. They constructed the Standard Book Numbering system (SBN), which was introduced in 1967. In 1970 the ISO, International Organization for Standardization, which consisted of several countries, adopted this standard system. It evolved into the ISBN numbering system and is now the standard in approximately 150 countries.
Books that were published prior to 1970 do not have ISBN numbers. These books may be rare and antique. But, just because they are labeled this way does not mean that they are valuable. The most basic of our economic terms, supply and demand, help us dictate the value of such books. A book found in abundance with little desirability to collectors will normally be worth less than a book that is scarce and in high demand. The demand for less common and more desirable books drives the price up. If you are looking to sell your rare or antique books then look to Abebooks.com or Powellsbooks.com. These are both great places to sell or just price the books. If you think that the books may be of more value than these sites give you, then you can try finding an ABBA (Antiquarian Bookseller’s Association of America) near you.