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var and let are both used for variable declaration in JavaScript, but they have some differences in terms of scope and behavior:

Scope:
Variables declared with var are function-scoped or globally scoped. This means they are accessible within the function or the global context in which they are defined.
Variables declared with let are block-scoped. They are limited to the block (a set of statements within curly braces) in which they are defined, such as loops, conditionals, and functions.

Hoisting:
Variables declared with var are hoisted to the top of their containing function or global scope. This means you can use a var variable before it's declared, but it will be undefined until the declaration.
Variables declared with let are also hoisted but not initialized, so you'll get a ReferenceError if you try to access them before their declaration.

Re-declaration:
Variables declared with var can be re-declared within the same scope without any error. This can lead to accidental overwriting of variables.
Variables declared with let cannot be re-declared within the same scope. Attempting to do so will result in an error.

Given these differences, it's generally recommended to use let (or const for constant values) over var in modern JavaScript development, as it provides better control over scope, reduces the potential for unintended behavior, and aligns with more predictable coding practices.