let

Followed by infinitive without to

Let is followed by object + infinitive without to.

• We usually let the children stay up late on Saturdays. (not … let the children to stay / staying …)
• She didn’t let me see what she was doing. (not … let me saw …)

Note the expressions let … know (= tell, inform) and let … have (= send, give).

• I’ll let you know my travel dates next week.
• Could you let me have the bill for the car repair?

Let go of means ‘stop holding’.

• Don’t let go of Mummy’s hand.

Not used in passives

This structure is unusual in passive forms; we prefer allow.

• After questioning he was allowed to go home.

With object + preposition / adverb particle

Let can be followed by an object and a prepositional phrase or adverb particle expressing movement.

• You’d better let the dog out of the car.
• Let him in, could you?
• Those kids let my tyres down.

This structure is also common in the passive.

• He was let out of prison early for good behaviour.

note

For let introducing first- and third-person imperatives (e.g. Let’s go for a walk; Let me see; Let the prayers begin), (see here).

For more about infinitives without to, (see here).