The expression !!0 evaluates to false. The ! operator (logical NOT) first converts its operand to a boolean and then negates it. The number 0 is falsy in JavaScript, so !0 evaluates to true (the negation of false). Then, !true evaluates to false. The double negation (!!) is a common idiom used to convert a value to its boolean equivalent, equivalent to Boolean(0). This technique is useful for explicitly converting values to booleans without changing their 'truthiness'.