These verbs all have the same meaning. The difference is in their grammatical structure:

LET + PERSON/THING + VERB (base form - without "to")

Examples:

I don't let my kids watch violent movies.

Mary's father won't let her adopt a puppy because he's allergic to dogs.

Our boss doesn't let us eat lunch at our desks; we have to eat in the cafeteria.

Oops! I wasn't paying attention while cooking, and I let the food burn.

Don't let the advertising expenses surpass $1000.

The simple past tense of let is also let; there is no change!

The verbs allow and permit are more formal ways to say "let." However, with allow and permit, we use to + verb:

I don't allow my kids to watch violent movies.

Our boss doesn't permit us to eat lunch at our desks.

Permit is the most formal, let is the least formal, and allow is in the middle.

With permit and allow, we can also say that something is or is not permitted/allowed:

Smoking is not allowed.

Employees are allowed to take a one-hour lunch break.

Passengers are not permitted to use cell phones during takeoff.

With a tourist visa, you are permitted to stay in the country for 90 days.

Problems Only 00s Girls Will Understand

Teen Girls and their Friends

For an adolescent, their friends hold a very special place in their lives. Every friend is important and leaving out one for the other is strict no no. This is what poses a problem when it comes to figuring out in what order to place friends on MySpace. The added problem here is that the more number of friends your account reflects, the more good it does for your profile. This means you cannot risk of hurting one friend by putting him/her in the wrong place on the MySpace order and losing them. Such a dilemma is it not? Parents will never understand it.