If you've decided to collect US postcards, one of the first things you'll discover is that it's not easy to tell how old it is.  The information below will give you a novice idea of the postcard eras.

PRIVATE MAILING CARD ERA (1898-1901).  The Private Mailing Card Act of 1898 required the following to appear on the cards: "Private Mailing Card-Authorized by act of Congress, May 19, 1898." The back was used strictly for the address. A blank area was frequently left available on the front (picture side) for a message.

UNDIVIDED BACK "POST CARD" ERA (1901-1907).  Beginning December 4, 1901, the word "POSTCARD" can be imprinted on back side. Only the address could be recorded on the back (non-picture) side.

DIVIDED BACK ERA (1907-1915).  Beginning 1907, the backside of the postcard has a line down the middle, providing an area for message and for address. The front displays an image across entire card with no borders. View cards are in a glossy litho format.

WHITE BORDER ERA (1915-1930).  Postcards continue to have a divided back. The front of card has a border - usually white -  around entire image.

LINEN ERA (1930-1944).  Cards are made of a linen type paper with a high rag content. The postcard has a textured feel.

CHROME ERA (1945 to date).  Vivid color photographs on postcards. Cards have a shine to them. Cards are dated by objects in photo.

CONTINENTAL ERA/MODERN (1970 to date).  Glossy photos on postcards.  Postcards are larger than previous eras, now at 4x6 inches.