When we talk about the value of something, especially something that is collectible, it is important to know that there are actually 2 different values that we can consider (and that are found in different ways) - its book value, and its market value.
Things (coins, cars, houses) usually don't have a single, fixed "value" or "price" that everyone agrees to. If you go to 3 different grocery stores, you'll probably find 3 different prices for the same items. For things that people commonly collect (like coins, comic books, or baseball cards), some person, group, or company has probably created a "price guide" - a book (or magazine, or Web site) which lists the different items and gives them an estimated value (usually based on a lot of research). A commonly-used price guide for cars is the Kelley Blue Book, for example. When you get the value for something from some kind of a price guide - whether from an actual book or a monthly magazine or a Web site - it is called the book value.
Book values are useful as estimates (for insurance, or for comparing the estimated values of several coins), but they are usually not what you could actually buy or sell a coin for.
The market value of a thing is what someone would actually pay for it, which can be more than or less than the thing's book value and can change frequently. I may have a coin that a book says is worth $100, but if nobody is willing to give me that much for it, is it really worth $100? Or I may have a coin that a book says is worth 25 cents, but it is very popular right now and I am able to sell it for $1. Finding the market value of a coin is more difficult, and requires you to do some research. It's also only really useful to know if you want to try to sell a coin (or are checking if a coin you want to buy is a good deal).
Source of article: Portland Coin
