Prefix and postfix increment/decrement operators differ in whether they increment/decrement the variable before or after assignment. With prefix (++i, --i), the operation is performed first before assignment. With postfix (i++, i--), the original value is assigned first before the increment/decrement. For example, if i=5, then ++i would result in i being 6, while i++ would still leave i as 5 but return 6.