There is a difference between stamp collectors and those who extensively study stamps, which is called philately. Most people enjoy collecting stamps as a form of recreation. They don't spend time worrying about minute details. Those who indulge in philately are typically those who tend to invest large amounts of money in the buying of stamps. They make it a point to understand the finer points of a stamp and the rarity or desirability of a particular stamp. Rare stamps are rising increasingly in value and for some this can be quite an investment.
There have been an incredible number of stamps that have been created over the decades. For one to have a complete comprehensive collection they would have to have literally thousands of albums to hold them all. Typically your average collector will limit their collection to a specific topic or types of stamps. Some collect only stamps from a specific country while others will look for those stamps from a certain time frame. Whatever the range that collectors are limiting themselves to, one can be certain that there will always be some very interesting pieces in the collection.
With the sheer number of stamp collectors there are today, there are now thousands of clubs and organizations for these collectors to exchange information about their passion. The Internet has also opened up huge opportunities for one to search for a particular stamp or investigate a certain type of stamp that they may be looking for. Just about any postal system all over the world has had some rare stamps. They can be postal errors or simply a very limited number that had been printed. One of the rarest stamps around is the 1-cent Z grill stamp. There are only two of these stamps known to exist. One is on display in a library in New York, under lock and key. The other one is available to collectors.
Stamp collecting began roughly in the 1800's. In the beginning it was considered mainly a child's hobby. It wasn't until the late 1800's that these children, now adults began to study existing stamps and read up on plate flaws and general production information. In the early 1900's there was a sharp increase in the number of stamp collectors when people found that there was value and profit in certain stamps. This encouraged people to begin looking for specific stamps. With the onslaught of Internet communication, emails and text messaging, it may be that stamps will grow even more in value as they become more and more scarce.