地平说是一种世界观，与地圆说相对，认为地表一块平面，而不是一块巨大的球面。这种观点是绝大多数民族自古以来所持有的观点。

直到古希腊时代，约前4世纪，许多古希腊学者开始利用科学（而不是基于宗教或者神话）讨论地球形状。后来，亚里士多德总结了3种方法来证明大地是球形的：

埃拉托斯特尼第一个提出公式计算了地球的半径，尽管由于当时的观测精度有限，其结果与今日之观测相差甚大，但表明当时的人们已经知道大地是球形的了。

此后，西方人大多数都认可大地是球形，托勒密创建的地心说即基于地圆说之上。中世纪时，罗马教会将地心说奉为正统，更加速了地圆说的传播。最后到地理大发现时代麦哲伦绕地球一周直接证明了地圆说，地平说才被彻底证明是错的。

The flat Earth model is an archaic conception of the Earth's shape as a plane or disk. Many ancient cultures subscribed to a flat Earth cosmography, including Greece until the classical period, the Bronze Age and Iron Age civilizations of the Near East until the Hellenistic period, India until the Gupta period (early centuries AD) and China until the 17th century. That paradigm was also typically held in the aboriginal cultures of the Americas, and the notion of a flat Earth domed by the firmament in the shape of an inverted bowl was common in pre-scientific societies.