1. A guide of United States Coins. (Red Book)-(Blue Book) 2. The complete encyclopedia of Colonial and US Coins. (Breen) 3. Krause (World Coins and Currency) General referrence is complete in these issues. They should not however be used as price guides. There are numerous books written on each collectible series. Many for varieties and errors. Too many to list here. Weekly and monthly magazines are also recommended for the collector to stay abreast of the current market.