A Boolean value is either true or false, and a comparison using a relational operator evaluates to a Boolean. AND is true only when both conditions are true; OR is true when either or both are true. Selection decides which parts of an algorithm run, and if-statements change the flow of control based on a Boolean expression. The same decision can be written in more than one way, and readability helps decide which way to choose. Rules can carry bias, so developers test and refine them with users in mind.