"What is Love" centers around two close families with sharply contrasting values. One consists of medical resident Lee Dae Bal, his mother and father and his younger sister Sung Shil and is conservative and patriarchic, the other consists of college student Park Ji Eun, her siblings Jung Eun and Jung Sup, her two maternal aunts and her parents. They are progressive, modern and utilitarian. This drama comically portrays the troubles that arise as these two families become quarrelsome in-laws by Ji Eun and Dae Bal's marriage and the conflicts that arise between Ji Eun and her in-laws, delivering a message about the importance of balancing traditional and progressive values.