Most games of Magic, especially casual ones, are played with constructed decks, made by the players before they arrive at game. Constructed formats, as opposed to Limited formats, allow players to build decks from the entirety of the legal cards available in the specified format. Which cards are legal in a constructed format is one of the main variations between the various formats. 
Examples of constructed formats in DCI-sanctioned tournaments include Standard, Extended, Modern, Legacy, Vintage, Block Constructed and Rainbow Stairwell. Players build their deck in advance of the tournament. Among casual players, many variants such as pauper and Commander are popular.
- Constructed decks must contain a minimum of 60 cards. There is no maximum deck size, however, the player must be able to shuffle their deck unassisted.
- Players may have a sideboard of at most 15 cards. Players may exchange cards out of their sideboard for cards in their deck after the first round of a match. Exchange may not be on a one-for-one basis however, the main deck must have at least 60 cards and the sideboard must not have more than 15 cards after exchanging.
- With the exception of basic lands (land cards that have the "basic" supertype) and cards like Relentless Rats, a player’s combined deck and sideboard may not contain more than four of any individual card, counted by its English card title equivalent.
- A card may only be used in a particular format if the card is from a set that is legal in that format or has the same name as a card from a set that is legal in that format.
- Cards banned in a specific format may not be used in decks for that format. Cards restricted in a specific format may only have one copy in a deck, including sideboard.
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 exactly 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.
Team Constructed tournaments use Unified Deck Construction rules: In addition of the usual construction rule, (with the exception of cards with the basic supertype) no individual card (based on its English card title) may be used by more than two player in the same team: For example, if one player is using Naturalize in a Team Constructed tournament, no other player on that team may have a Naturalize in his or her deck or sideboard.
Originally, Unified Deck Construction allowed for an individual card to be used by more than one players in the team, as long as the team's combined deck/sideboard contain less than four of them (unless the card is restricted or cards with text that specifies otherwise). UDC rules were modified to the current configuration (only 1 copy of individual card) during the 2016 World Magic Cup (accompanying the format change). WotC are hoping to "level the playing field" and reduce affordability as a potential restriction of teams' choices in their decks as Modern is used as the construction portion. 
- Reid Duke. (April 27, 2015.) “An Introduction to the Popular Constructed Formats”, magicthegathering.com, Wizards of the Coast.
- Helene Bergeot. (Feb 7, 2016.) “WMC and WMCQ Changes Announced at PT Oath of the Gatewatch”, magicthegathering.com, Wizards of the Coast.