Deltiology (from Greek δελτίον, deltion, diminuitive of δέλτος, deltos, "writing tablet, letter"; and -λογία, -logia) is the study and collection of postcards. Compared to philately, the identification of a postcard's place and time of production can often be an impossible task because postcards, unlike stamps, are produced in a decentralised, unregulated manner. For this reason, serious collectors may choose to limit their acquisitions to cards by specific artists and publishers, or by time and location.
Picture postcards (PPCs) can be assigned to "the Golden Age of Postcards" (1898-1918), the time of the linens (circa 1930-1950), or to the modern chromes (after 1940), Modern chromes are color photographs and thus differ from photochromes generated from black and white photographs prior to WWI. PPCs can also be differentiated on the basis of other features: undivided backs are typical for c1901-1906, and divided backs for c1907-1915, while white border cards are common from c1915-1930.
Deltiologists, as postcard collectors are called, collect for a variety of reasons. Some are attracted to the postcards themselves and then narrow down their interests. Others are interested in something in particular, such as Ballet, and then decide to collect Ballet related postcards as a way to augment their interest in Ballet.
Collectors may find PPCs at home in boxes, attics, or scapbooks, generate their own on trips and vacations, and acquire them from stores, fleamarkets, the internet, or other collectors.
A number of artists have become recognized for the creation of postcards and certain publishers specialize in the production and printing of PPCs.