The Hardy Boys, Frank and Joe Hardy, are fictional teenage brothers and amateur detectives. Frank is eighteen (sixteen in earlier versions), and Joe is seventeen (fifteen in earlier versions). They live in the city of Bayport on Barmet Bay with their father, detective Fenton Hardy, their mother, Laura Hardy and their Aunt Gertrude. The brothers attend high school in Bayport, where they are in the same grade, but school is rarely mentioned in the books and never hinders their solving of mysteries. In the older stories, the Boys' mysteries are often linked to their father's confidential cases. He sometimes requests their assistance, while at other times they stumble upon relevant villains and incidents. In the Undercover Brothers series (2005-2012), the Hardys are members of and receive cases from American Teens Against Crime.
In each novel, the Hardy Boys are constantly involved in adventure and action. Despite the frequent danger, the boys "never lose their nerve. They are hardy boys, luckier and more clever than anyone around them. They live in an atmosphere of mystery and intrigue. There were so many assorted felonies committed in a simple American small town. There were murders, drug peddling, race horse kidnapping, diamond smuggling, medical malpractice, big-time auto theft, even hijacking of strategic materials and espionage. All were conducted with Bayport as a nucleus. With so much in common, the boys are so little differentiated that one commentator facetiously describes them as "The boys' characters basically broke down this way – Frank had dark hair; Joe was blond." In general, however, "Frank was the thinker while Joe was more impulsive, and perhaps a little more athletic." The two boys are invariably on good terms with each other and never engage in sibling rivalry, except in the New Hardy Boys Casefiles series.