The combat rules for 5th Edition Dungeons and Dragons are much simpler than previous editions. This is a quick reference guide to the new rules. Refer to the complete rules (which can be downloaded for free here) for more detailed information. This is my own interpretation of those rules. Refer to the DM notes at the end for my house rules.

Each round represents 6 seconds in the game world. Anything a person could reasonably do in 6 seconds, your character can do in 1 round.

Each round, during your turn, you can move and take one action.

• You don’t have to move, but if you choose to, you can move a distance up to your speed. You can move before or after you take an action, or you can move first, take an action, and then move again, as long as the total distance moved doesn’t exceed your speed.
• You don’t have to take an action during your turn, but if you choose to, you can attempt to do anything that could be accomplished in 6 seconds or less. The most common action taken in combat is the attack action. See below for a list of actions that can be performed in combat.
• If your action permits multiple attacks, you can move between attacks so long as you haven’t used all of your move distance based on your speed.
• Your move can include jumping onto or off of things, jumping over things, climbing walls or ropes, swinging on ropes or chandeliers, or moving in any way that your character is capable of such as swimming or flying for example.

You can interact with one object as part of either your move or your action.

You can manipulate the object in an uncomplicated way. Some examples include:
•    Draw or sheath a weapon
•    Draw Two One-Handed Weapons [You can normally draw only 1 weapon for free on your turn. Dual Wielder lets you draw 2.]
•    Transfer an item from one hand to the other
•    Load a crossbow
•    Retrieve or put away a stored item*
•    Pick up an item
•    Move an object
•    Open a chest
•    Open a door
* You may only retrieve an item if it was stowed for easy access. If you must dig through your backpack to find something inside, it may require use of an action to retrieve it.
Doing more than one of these things requires the use of an action.

As part of your move or your action, you can do things that take little or no time and don’t interfere with your movement.

These activities take very little time, though there may be limits to the number you can perform in a turn. Examples include:
•    Drawing ammunition for use with a ranged weapon (such as arrows, bolts, sling bullets, or shuriken).
•    Dropping an item to your feet or within 5 feet of your current location.
•    Dropping to a prone position. (Standing up from prone, however, takes half of your movement for the turn.)
•    Speaking (you can always speak, even when it isn’t your turn – within reason.)

You may be able to take an additional, bonus action.

• A special ability, spell, or other feature of the game may allow you to do something as a bonus action. You are only allowed one bonus action in a round.
•    Example: If you have a short sword in one hand and dagger in the other, after using your action to attack with the sword, you can use a bonus action to attack with the dagger (refer to the rules on two-weapon fighting.)

You are allowed one reaction each round.

A reaction is an action that is triggered by an external event.

• A special ability, spell, or other feature of the game may allow you to react to a specific triggering event.
• If an opponent attempts to move past you or attacks you and then attempts to move away, you get a free swing at him. This is called an opportunity attack, and it is the most common reaction.
• Another example would be a wizard’s feather fall spell that is triggered when the wizard is pushed over a cliff, or steps into a pit trap.
• Your reaction does not have to occur during your turn, but can occur at any time during the round. If it occurs during another’s turn, his turn is suspended until your reaction is resolved.

Surprise

If surprised, you lose your turn for the first round of combat. After your turn, you are no longer surprised so you can use a reaction after your turn has passed, even during the remainder of the first round.

Actions in Combat

During your turn in a combat round, you can perform any one of the following actions.

Attack

You can make one melee or ranged attack. Some features may allow you to make more than one attack with this action.

Cast a Spell

You can cast any spell that you are capable of casting that has a listed casting time of one action.

Note regarding components: Retrieving the required material (M) component from a pocket or pouch is included in the “Cast a Spell” action. If the spell also has a somatic (S) component, you can perform the required hand gestures while holding the material component in that same hand. Therefore, if you are holding two weapons, or a weapon and a shield, at the beginning of your turn, you can sheath one weapon (refer to “interact with one object” above) and then draw the material component and cast the spell all in the same round. [A material component is not consumed with the casting of the spell, unless the spell description specifically says that it is.]

Dash

Rather than performing any other action, you spend the entire round moving. This allows you to move twice as far this round. It is effectively a double move action. [You use your dash action to move your speed then use your move to go that distance again.]

Disengage

If you start the round within 5 feet of an opponent that can see you, you can use this action to move away from him without provoking an opportunity attack. [The disengage action does not include a move. You use the disengage action to avoid an opportunity attack while you use your move to travel up to your speed.]

Dodge

This is a total defense action. You spend the round trying to avoid being hit. Until the start of your next turn, any attack roll made against you has disadvantage if you can see the attacker, and you make Dexterity saving throws with advantage.

Help

You can use your action to help an ally attack an opponent within 5 feet of you. You don’t make an attack yourself, but when your friend attacks, his first attack roll is made with advantage.
Or you can help him with any other task. If you are in position to do so, and your assistance could reasonably be seen to be of help, he will gain advantage on his ability check to accomplish the task.

Hide

The act of hiding requires an action to attempt. You must make a Dexterity (Stealth) check to see if you successfully hide from your opponents.
Additional information regarding the hide action here: Stealth and Hiding

Ready

Rather than taking and action during your turn, you wait for some specific event and then take your action as a reaction. You can still move up to the distance indicated by your move rate, but you can take no other action this round. You must specify two things –
1) What the triggering event will be.
This can be anything you think might happen that you can observe. If the event occurs before the start of your turn on the next round you can perform your readied action at that time. Some examples could be: If the sniper sticks his head up, If more Orcs come around the corner, If the rope brakes, If the water level rises, If the evil magic user starts to cast a spell, If the guard spots the thief, If the prisoner attempts to escape.
2) What action you will take.
This can be any of the combat actions.
Note that this action will be a reaction and you can only have one reaction per round. This means that if you take another reaction, you lose your readied action. Conversely, if you use your readied action you can have no other reactions this round.
• If the triggering event occurs, you can choose to not take your readied action.
• If you choose Dash as a readied action, you can move up to your move rate.
• If you choose Cast a Spell as a readied action, you cast the spell during your turn but hold off on releasing the energy of the spell until the triggering event occurs. You must concentrate to hold the spell’s energy. Anything that breaks your concentration before the final release of the spell’s energy results in the loss of the spell. If the triggering event doesn’t occur this round, you can continue to hold the spell with continued concentration into the following round, or you can cast it as an action on your next turn, or you can lose it.

Search

You can use your action to attempt to find something. The DM might require you to make a Wisdom (Perception) check or an Intelligence (Investigation) check.

Use an Object

An object may require an action for you to use it, or you may need to use this action to interact with more than one object in a round.

Improvised Action

There are many more things that a combatant could do during a round than can be accounted for in the above actions. When you want to attempt something that is not covered by any of the above actions, you can use an improvised action.

Examples of an improvised action:

“I want to pull the rug out from under that guy.”
“I want to jump on the monster and attack him with my sword while I ride on to his back.”
“I want to talk them into surrendering.”
“I want to break that flask the bad guy is holding.” (attack an object)
“I want to slide down the stairs on my shield while I fire arrows at the enemy.”
“I want to intimidate then into running away.”
“I want to grab that piece of folded parchment that is sticking out of his vest pocket.”
“I want to slide under the table and stab that guy in his ankle with my dagger.”
“I want to sheath my sword and walk up to that guy and tweak his nose.”
“I want to hit that rope with my arrow in such a way as to cut the rope and let the body that is hanging from it fall to the ground.”
“I want to disarm my opponent.” (This could be a called shot to the hand, shattering an opponent’s weapon, severing a spear shaft, entangling a sword arm, or using the flat of a blade to smack a weapon from an enemy’s hand.)
“I want to push him into the pit.” (Use the rules for “Shoving a Creature” – this could include shield bashes, tackles, bull rushes, overruns, tables hurled into enemies, doors smashed into opponents on the other side, and so on. Generally speaking, this could be any attempt to use brute strength to move an opponent. Any attempt to shove creatures off a nearby cliff, through a railing, out a chapel’s stained-glass window, and so on will allow the creature a dexterity save.)
“I want to trip that guy.” (This could be any attempt to knock an enemy off its feet. Whether it’s hooking an enemy’s leg, stabbing a kneecap, knocking an opponent off-balance, hurling an enemy away, sweeping an enemy’s legs, or some other maneuver, this improvised action would allow the warrior to knock an enemy prone.)

The following rules apply to improvised actions:
1. You must explain the improvised action to the DM. The DM may rule that what you want to do will require more than one round, or that it is simply impossible (you can’t fire an arrow into the sky and hit the moon). He may ask you to be more specific regarding the action you want to take and how the action will achieve the results you want.
2. The improvised action can also include all or part of your move. Successfully jumping on – or diving into a creature will give you advantage on the attack roll. A failed attempt results in your move stopping at the point there the attack takes place and may grant your opponent an advantage on his next attack against you.
3. To perform the improvised action the DM will normally have you make an ability check. The DM will assign an appropriate difficulty class and will explain possible consequences if the attempted action fails. For example, if you attempt to jump off of the balcony onto the monster in the center of the room and miss you may end up prone.

Most improvised actions can be resolved as simple contests.
Player: “I want to try to [describes some form of physical contest other than an attack roll].”
DM: “Okay, make a Strength (Athletics) check.”
DM compares result to opponent’s Strength (Athletics) or Dexterity (Acrobatics) check, perhaps giving someone advantage or disadvantage.

DM Notes: Some of the information above deviates somewhat from the official rules. You can consider these to be my House Rules.
Retrieving a stored Item – This should only be allowed as part of your move or action if you don’t have to dig through your backpack to find it.
Speaking – Should be allowed at any time
Disengage – I will only allow this action if you are currently engaged in combat and want to withdraw without provoking an opportunity attack.
Help – It only makes logical sense to be able to help another if there is some action that you could take that might possibly be of help to him.
Improvised action – I got rather wordy here, but I think these should be encouraged.