Advertising , Agriculture , Amusement Parks , Animals—cats, dogs, wild, zoo, alligators, cows, pigs, rabbits, etc. , Architecture , Art , Art Deco , Artist Signed , Beer , Calendars ,  Children ,   Colleges and Universities , Comics , Cowboys , Crafts—woodworking, folk art, quilts, jewelry, baskets, decorative painting, knitting, etc. ,  Drinking ,  Entertainment—entertainers, theaters, shows ,  Ethnic ,   Exaggeration ,  Expositions and World's Fairs ,  Events ,  Fairs ,  Fashion ,  Fantasy ,  Fishing , Food , Gambling  , Greetings—general, birthday, mottos  ., Historical—places, events  , Holidays—New Years, Valentines, St. Patrick's Day, Easter, Fourth of July, Halloween, Thanksgiving, Christmas , Homes—exteriors, interiors, decoration, furniture   ,Hospitals ,  Hotels ,  Hunting ,  Indians ,  Industry ,  Interiors ,  Large Letters ,  Maps ,  Military—WWI, WWII, Army, Navy, comics ,  Motels ,  National Parks ,   Nature—birds, wildflowers, insects, trees, etc. , Novelty , Occupations , Parades ,  Patriotic ,  Photography ,  Political—action, elections, politicians, presidents , Postal—post offices, mail, stamps, postcards , Posters ,  Real Photos , Religious , Restaurants ,  Risque ,  Rivers ,   Roadside ,  Romantic ,  Royalty , Scouting   , Snowmen , Space   , Sports—baseball, football, stadiums, skiing, skating, golf, etc. ,  Statues ,  Stores , Street scenes ,  Tacky ,  Transportation—autos, trains, planes, buses, trolleys, ships, highways, depots, airports , Travel ,  Women ,  Women's Rights  , Alphabet Letters ,  Artists & Painting, Astrology, Astronomy,  Banners & Pendants, Barbers, Blank Destinations,  Boy Scouts ,  Butterfly Views,  Calendars,  Camping, Card Games,  Clocks & Watches,  Coffee & Tea,  Cooking , Correspondence Cards,  Crooks,  Dancing,  Days of the Week,  Death, Dentists,  Devils,  Disasters,  Divers,  Doctors & Medicine,  Farming,  Firemen,  First Day Covers,  Flags,  Geology, Rocks & Minerals,  Hobos,  Hold To Light,  Interesting Cancels,  Lawyers & Legal,  Lighthouses,   Logging,  Mining,  Money,  Months, Names,  Numbers & Math,  Oil Wells,  Outhouses, Phrases & Sayings, Poems, Police,  Post Card Clubs,  Postal, Prisons,  Puzzles,  Radio,  Rally Day,  Religious, Scales, Weight,  Scenic,  Schools & Education,  Seasons,  Sewing,  Shoes,  Silk & Fabric Applique,  Spanking,  Stamps,  Swastikas,  Telephones  , Time of Day,  Tobacco,  Typewriters,  Umbrellas & Parasols,  Windmills,  Work & Office, Years, Airlines, Airports, Amusement Parks, Angels, Arcade Cards,  Asylums and Institutions, Barber Shops, Bathing Beauties, Baseball, Beer & Breweries, Billiards, Black Americana, Boxing, Boy Scouts, Cars, Autos, and Trucks, Chimney Sweeps, Circus, University and College Girls Series, Civil War, Coca-Cola, Trolley, Train and Bus Depots and Stations, Doctors and Nurses, Dressed Animals, Erotic, Exhibitions, Factories and Mills, Fire Engines, Firemen, Fishing, Football, Gambling, Poker, Gas Stations/Service Stations, Hockey, Horse Racing, Hunting, Immigration, Indians / Native American, KKK, Main Street Scenes, Masonic, Mermaids, Mining (Gold, Silver, etc.) Motorcycles & Bicycles, Banks, Nudes, French Nude, Ocean Liners, Political, Presidential, Prisons & Jails, Propoganda (US & Foreign), Railroad, Red Cross, Restaurants, Retail Stors, Rodeos, Route 66, Ships, Snowmen, Sports, Surfing, Tobacco, Smoking, Town Views, Trade Cards, Trains, Trolley, Trollies, War Ships, Military, Watches & Clocks, Cowboy, Western, Veterinarians 

These are some popular postcard collecting topics. Don't limit yourself to these topics—just collect anything that interests you. Many people collect topics related to their profession or other hobbies.

The dating of the postcard for years or eras of issue can be accurately determined if the card is studied for identity points.There were seven eras for the postcard industry and each one has distinguishing points to help establish its respective identity

The Pioneer Era began when picture postcards were placed on sale by vendors and exhibitors at the Colombian Exposition in Chicago, May 1893. The cards from this era are relatively scarce.On May 19, 1898, the government gave private printers permission to print and sell postcards. . It is easy to identify these because of the inscription.
On December 24, 1901, permission was given for use of the wording "Post Card" to be imprinted on the backs of privately printed cards. All cards during this era had undivided backs of privately printed cards.   This era came into being on March 1, 1907. The divided back made it possible for both the address and the message to be on the back of the card.
The White Border Era brought an end to the postcard craze era. . These are easily distinguished by the white border around the pictured area.   Publishers began using a linen-like paper and Until recently, collectors considered these cards very cheap. Now they are very popular with collectors of roadside America, Blacks, Comics, and Advertising. Views are also becoming more popular . "Modern Chromes," as the postcard fraternity now calls them, were first introduced in 1939.  The growth of this group has been spectacular in recent years, so much so that there are now many postcard dealers who specialize only in chromes.
Real Photo postcards were in use as early as 1900. It is sometimes very hard to date a card unless it has been postally used or dated by the photographer. Careful study of photo cards is essential to make sure they have not been reproduced.
 

Grading Guide
I = Nearly perfect.
II = Excellent, only light handling or wear.
III = Fine, clean, collectible with some
edge wear and /or possible minor faults.
IV = Card is decent but shows wear
and/or faults. Not unattractive
V = Lower grade.