Proudly regarded as the classic suit’s formal cousin, a three-piece suit comes with its own unique set of rules and expectations. As you might have guessed, the distinguishing feature to a three-piece suit is the inclusion of a vest, sometimes referred to as a waistcoat. This element is sometimes a source of trepidation to the gentlemen out there who are comfortable with the familiar two-piece option yet are a bit perplexed by the etiquette thrust upon them with this additional garment.