Most games of Magic, especially casual ones, are played with constructed decks, made by the players before they arrive at game. There are also multiple formats that are played with constructed decks in DCI-sanctioned tournaments; examples include Standard, Extended, Modern, Legacy, Vintage, Block Constructed and Rainbow Stairwell. Many variants such as pauper and highlander are popular among casual players.
In constructed, both players involved in the game play a deck of at least 60 cards, of which no cards except basic lands are present in more than four copies. A general convention is to play 20-25 lands, and 35-40 spells, but there is wide variance in this aspect.
In order to have the deck play consistently, many constructed decks, or at least most of those used in tournaments, run four copies (known as a playset) of each card important to the deck, and run a maximum of sixty cards. This causes the important cards to be drawn on a more regular basis, and helps the deck to be more reliable.
With the advent of the internet, the sharing of decklists (known as netdecking) has become more and more prevalent, reducing some of the creativity and thought players have to put into the construction of their decks. Originally, Wizards of the Coast opposed this trend, but has embraced it in recent years, even running a daily deck feature on the game's website. The presence of netdecking often causes a number of powerful deck archetypes to emerge. Through netdecking, many similar or identical decks following certain popular strategies will often be present at a tournament. Because of this, the metagame of a constructed format is much more important than the metagame of a limited format. This leads to decks sometimes being built simply because they will be good against popular decks; for example, if both kithkin and faeries are popular decks in standard, a player may be more inclined to run a giant deck with multiple copies of Thundercloud Shaman. Decks that are not very popular or common in the metagame are called Rogue decks.