What do you call a person who collects postcards?

A deltiologist is a person who collects postcards. Postcards became popular in the United States in the early 1900s both as a means of communication and as a collectible.

Deltiologists tend to focus their collections on particular themes, such as pictures by famous artists. Some collect a particular type of postcard, such as hold-to-light cards that are made using both tissue and regular paper. Due to the variety of topics that are depicted, postcards are also desirable to collectors of photography, war memorabilia and advertising. The monetary value of a postcard as a collectible is determined by factors such as age, condition and subject matter.