Does a concentration spell still require concentration when triggered by Contingency?

Question

Does a spell that normally requires concentration, but which is cast with and triggered by Contingency, still require concentration once it begins?

Part of the reason I ask is in comparison with a similar situation, in which a concentration spell cast into, and then triggered by, a Glyph of Warding lasts for full duration without concentration being required of anyone.

Answer 1

Yes, the contingent spell will still require concentration.

In 5e spells do only what they say they do. Contingency says nothing about modifying the effects of the contingent spell.

You cast that spell--called the contingent spell--as part of casting contingency, expending spell slots for both, but the contingent spell doesn't come into effect. Instead, it takes effect when a certain circumstance occurs. [...]

The contingent spell takes effect immediately after the circumstance is met for the first time, whether or not you want it to, and then contingency ends.

The only things contingency changes about the spell are that the effect is delayed until the condition is met and the target is changed to only target the person who cast contingency. Nothing about changing concentration or duration.

Compare this to Glyph of Warding (a spell that is similar in some ways to contingency) which specifically says:

If the spell requires concentration, it lasts until the end of its full duration.

Since there is no such wording in contingency, there is no reason to think that it does change anything to the contingent spell except what it is written in the spell effect already. Thus, the contingent spell will require concentration once it is triggered.

Official ruling - concentration is required

Jeremy Crawford agrees with the above in this clarification:

Q: Contingency: if the spell stored requires Concentration, do you need to maintain concentration on it when Contingency is triggered?

A: The contingent spell stored by contingency doesn't come into effect until its condition is met. When that happens, the contingent spell functions as normal, including its duration.

Answer 2

The wording of contingency is a bit vague when it talks about the "effect" of the spell. Discusson about what similar wording exactly means is common (for example about rings of spell storing). The book does not clarify this, but we can fall back on a bit of logic here:

1. The spell should have its original duration. Nothing says it changes, and if it did what would it be?
2. Concentration is an attribute of a spell's duration. It is listed there on p.203 of the PHB and in that row in every spell description.

So yes, concentration spells cast as part of contingency will require your concentration when activated.