What are these "obsolete" bank notes?
This was the paper money that was used in the United States between the end of the Revolutionary War and the Civil War (1780s-1860s). It was issued by private banks, states, counties, towns, merchants, factories and private individuals. Standardized, Federally-issued United States government paper money started to replaced this mixture of notes in circulation in 1861 and little of it was left in circulation by the end of the 1860s. Most of the notes printed were destroyed after use and upon redemption but some groups and many individual notes, both used and unused were saved for various reasons. These are what we collect today.
Why haven't I ever seen these things before?
Even though millions of these notes were printed during the 19th century, the vast majority (over 99%) were destroyed once they had served their purpose. This was simple security and common sense as destruction was the easy way to assure that used notes wouldn't become reused and circulated in any unauthorized manor. So, they are scarce as a collectible and when a collectible is scarce, it's hard to promote.
Collecting of bank notes is considered a part of numismatics which including the collecting of coins, bank notes, tokens, medals and like items. Collecting obsolete currency is a small part of the bank note field. Most popular paper money categories include US Small Size notes (current size), US Large Size notes (Pre-1928 size), US National Bank Notes (1865-1935) and Worldwide Currency. Obsolete currency is one of the smaller categories but gaining in numbers rapidly. This is causing upward price pressure in recent times, more so than in most other areas of numismatics.
Where can I learn more?
Internet: Do some searches. Explore other currency dealer websites to get a feel for what's out there. Look on eBay and learn what is common and get a feel for pricing. SPMC (Society of Paper Money Collectors) and ANA (American Numismatic Association) are the leading collector organizations and have useful websites.
Books: "Standard Catalog of US Obsolete Bank Notes" by James Haxby is the most comprehensive reference covering all states. 2000+ pages, 4 volumes, published 1987. Limitations: Only lists banknotes, no scrip. Prices outdated. Price/availability. Out of print, 4 volume sets currently sell $500-$700 but CD version is now available at around $150-$175. A wise investment if you want to collect more than a narrow area.
Individual state books covering most of the states that issued obsolete notes and scrip have been published in recent years. Some are better than others but all cover the wide variety of scrip issued, so tend to be more complete than Haxby. Price and availability varies but most books can be found with a bit of effort in the $20-$50 range. Please inquire if you have specific questions about any state books.