留基伯（希腊文：Λεύκιππος）是公元前5世纪古希腊哲学家，也是率先提出原子论（万物由原子构成）的哲学家，也是德谟克利特的老师。一说他出生在米利都，一说阿布德拉。他的学说受到三个哲学家的影响——芝诺、恩培多克勒、阿那克萨哥拉。约公元前440年-前430年，他在阿布德拉成立了一个学校，而德谟克利特也就是在这所学校就学的。

Leucippus (/luːˈsɪpəs/; Greek:Λεύκιππος, Leúkippos; fl. 5th cent. BCE) is reported in some ancient sources to have been a philosopher who was the earliest Greek to develop the theory of atomism—the idea that everything is composed entirely of various imperishable, indivisible elements called atoms. The name Leucippus is often associated as master to pupil with that of Democritus, the philosopher who was also touted as the originator of the atomic theory. However, a brief notice in Diogenes Laertius’s life of Epicurus says that on the testimony of Epicurus, Leucippus never existed. As the philosophical heir of Democritus, Epicurus's word has some weight, and indeed a controversy over this matter raged in German scholarship for many years at the close of the 19th century. Furthermore, in his Corpus Democriteum, Thrasyllus of Alexandria, an astrologer and writer living under the emperor Tiberius (14–37 CE), compiled a list of writings on atomism that he attributed to Democritus to the exclusion of Leucippus. The present consensus among the world's historians of philosophy is that this Leucippus is historical. The matter must remain moot unless more information is forthcoming from the record.