In summer 2013 Steam launched a new feature, trading cards. Steam users receive those cards by playing certain games. They may then buy, sell or trade cards with other Steam users. The cards have no effect on any game play whatsoever, they are solely meant for collectors and those willing to boost their Steam "XP" and "level".
How do they workEdit
Civilization V is one of the many games that will grant users trading cards. As with all other participating games, the players have no say over when and what cards they will receive: the cards are random and granted only based on play time. Initially for each participating game each player may only receive about half of the cards that together make up a deck. In the case of Civilization V, the deck has eight cards, which is a very typical size for a deck. Once all card drops are exhausted and the player has received their four cards, the rest need to be acquired by trade or by using the Community Market. Note that players may also receive and own duplicate cards.
Once a full deck has been acquired, the user may use the deck to craft a badge. At most five complete decks can be consumed to craft a new badge. Consuming the deck grants the user "Steam XP" which progresses the user towards their next "Steam Level". Steam Levels are a summary of user's badges and participation in Steam events, such as Summer Sales. In addition, crafting a badge will grant the user some random small items to be used in Steam, such as new emoticons (related to the game whose trading cards were used) to be used in the Steam chat.
Along with the regular cards there are also rare foil cards which look a bit different to the regular ones but work otherwise the same way. Foil cards can be used to build their own deck, they do not mix and match with the regular cards. The foil versions of the cards are typically sold for 4 to 10 times the price of a regular card.
With every game the cards have a small image and a large, poster-like image that you can see when you have acquired that card and then click on it.