In Greek mythology, the Apple of Discord (Ancient Greek: μῆλον τῆς Ἔριδος) was a golden apple dropped by Eris, the goddess of strife, at the wedding of Peleus and Thetis. It sparked a vanity-fueled dispute among Hera, Athena, and Aphrodite that led to the Judgement of Paris and ultimately the Trojan War.

In common parlance, the "apple of discord" is the core, kernel, or crux of an argument, or a small matter that could lead to a bigger dispute.

In the Eixample district of Barcelona, there is a block nicknamed in Spanish La manzana de la discordia (Catalan: Illa de la Discòrdia). The reason for this usage is that the word manzana means both "apple" and "city block" in Spanish. It was so named ("block of discord") because it features four different interpretations of Modernisme architecture: Antoni Gaudí's Casa Batlló, Lluís Domènech i Montaner's Casa Lleó Morera, Josep Puig i Cadafalch's Casa Amatller, and Enric Sagnier's Casa Mulleras.

In some later sources, Eris inscribed on the apple "for the fairest" or "to the most beautiful" before tossing it. The most popular version of the inscription in Greek is τῇ καλλίστῃ (transliterated: tē(i) kallistē(i), "for/to the most beautiful"). Καλλίστῃ is the dative singular of the feminine superlative of καλός, "beautiful". In Latin sources, the word is formosissima.

In an attempt to rationalize the myth, Ptolemaeus Chennus wrote that instead of an apple, the three goddesses fought over which would get a man named Melus ("apple") as her priest, with Paris deciding in favour of Aphrodite.