Few rules in Magic have more uses than APNAP order. Read on to find out how it works, or just to get a refresher!

The Basics

A Player is "one of the people in the game." (Comp. Rules 102.1)

The Active Player (sometimes referred to as "the attacking player") is the player currently taking their turn. (Comp. Rules 102.1)

The Non-Active Player is any player in the game whose turn it currently isn't. (Comp. Rules 102.1)

APNAP stands for "Active player, non-active player" and refers to a way of ordering choices.

How Does it Work?

"If multiple players would make choices and/or take actions at the same time, the active player makes any choices required, then the next player in turn order makes any choices required, followed by the remaining nonactive players in turn order." (Comp. Rules 101.4)

In other words, if something goes on the stack that requires more than one player to make a choice, the choices occur in APNAP order.

Example: it's your turn (you're the Active Player). You play a Fleshbag Maurader, which says "Each player sacrifices a Creature". Because you are the Active Player, you must choose first and tell the table or otherwise represent which Creature you will sacrifice. Then the next person in turn order (almost always the person to your left, but not every time) will choose, and so on until every player has chosen.

It works the same for two-player games, multiplayer games, and for subsets of players. If, for example, you force two of your opponents to sacrifice a Creature while you're the Active Player, they would choose their Creatures in APNAP order too - which is simply turn order. Then everyone sacrifices their Creatures at the same moment.

Why Does This Matter?

One word: information. The last person in APNAP order makes their choice with the most information; the Active Player makes it with the least. Them's the breaks.

It can also be very helpful when a game gets complicated. In most casual games of Commander, it doesn't actually matter if you're careful with APNAP when someone plays a Fleshbag Maurader - but sometimes it does. When it does, you can simply use APNAP to clarify the process and keep everything above board.

That's Not So Bad

Nope, it's not. But it can get more complicated. Here's how.

This works for any situation where more than one player has to make a choice at the same time, unless the card says to do it differently.

It also works when multiple things happen at the same time but they can't. The best, and probably most common, example of this is Upkeep.

Example: It's just become your turn. You untap your Creatures, Lands, and anything else to be untapped, and you move to your Upkeep phase. You have a card that says "at the beginning of your Upkeep, draw a card" and another that says "at the beginning of your Upkeep, create a 1/1 Soldier Token." You are the Active Player, so you get to choose the order in which those two things go on the stack, and they will then resolve in reverse order.

However, one of your opponents has an effect that says "at the beginning of each Upkeep, make a Treasure Token." In that case, you have two Triggered abilities, and your opponent has one. They all need to happen at the exact same moment. So, they go on the stack in APNAP order - yours first, in whichever order you choose, then your opponent's. The opponent's resolves first (they make a Treasure), then yours (I'd draw the card then make the dude, but that's just me).

One important note here: you cannot alter this order. If you (the Active Player) have an Upkeep ability which lets you discard, and your opponent has an ability which makes you lose life equal to the number of cards in your Hand, you can't reorder the stack so you discard first. You're the Active Player, so your stuff goes on the stack first, then resolves last. Sorry.

This matters in lifegain/loss situations too. If you're the Active Player and have something that gains you life, but your opponent does something which causes you to lose life, APNAP order means your life gain goes on the stack first, then their life loss. Their life loss resolves first (last in, first out), and if that puts you at or below zero life, you'll lose the game before you gain any life.

In the event multiple players have things happening while starting the game, the starting player is considered the Active Player.

One more stupidly complicated thing. If you're going around APNAP order making a choice, and one person's choice forces someone else earlier in the turn order (Active or non-active) to make a new choice, APNAP order is restarted with the new choices.

Example (from mtgsalvation.com forums): Your opponent has a planeswalker and there are some number of Creatures on the Battlefield. You cast Pyroclasm, and your opponent casts Blood of the Martyr in response. Assuming both resolve, you will have no replacement effects to apply. Then, your opponent chooses to apply Blood of the Martyr's effect to redirect some damage to himself to save one (or more) Creatures. Now that damage is being dealt to your opponent, you have a replacement effect to apply - namely, redirecting that damage to his or her planeswalker.

The situation in which this rule would come up would be pretty wild, but it could happen. Note this doesn't alter previously-made changes, just that APNAP restarts with the new set of choices. All previous choices remain.

Please, No More

Teams are a thing in Magic, and when you have them, you treat the Active team as the Active Player. So, the Active Team will make all their choices first, then the non-active team(s) will make theirs, then everything will resolve as it should in the reverse order.

Why Should I Care?

Truly, APNAP demystifies complicated interactions. If you understand the stack and apply APNAP, you can untangle the most tangled web of activated and triggered abilities, Counterspells, all in the midst of Combat. In that sense, it is one of the most powerful tools you possess to better understand this game.