# [−]Keyword let

The `let` keyword.

The `let` keyword is used to declare a variable.

Example:

    let x = 3; // We create a variable named `x` with the value `3`.Run

By default, all variables are not mutable. If you want a mutable variable, you'll have to use the `mut` keyword.

Example:

    let mut x = 3; // We create a mutable variable named `x` with the value `3`.

    x += 4; // `x` is now equal to `7`.Run

For more information about the `let` keyword, take a look at the Rust Book.

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