葛梯尔问题（英语：Gettier problem），又译为盖提尔问题，是现代知识论中的一个关于知识的定义的问题。1963年，美国哲学家爱德蒙德·葛梯尔（Edmund Gettier）在一篇只有三页纸的论文中质疑当时哲学界公认的知识的定义：知识是得到辩护的真信念（也称为知识三要素，或“JTB理论”）。他的论文标题是：“得到辩护的真信念就是知识吗？”。在论文中，葛梯尔提出了两个反例，说明即使是得到辩护的真信念，也未必是知识。这篇论文引发了哲学界对于知识定义的一系列争论，并导致了葛梯尔问题的出现：“应当怎样补充或修改知识三要素，才能完整地定义知识的概念？”

The Gettier problem, in the field of epistemology, is a landmark philosophical problem with our understanding of knowledge. Attributed to American philosopher Edmund Gettier, Gettier-type counterexamples (called "Gettier-cases") overturned the long-held justified true belief (or JTB) account of knowledge. On the JTB account, knowledge is equivalent to justified true belief, and if all three conditions (justification, truth, and belief) are met of a given claim, then we have knowledge of that proposition. In his three-page 1963 paper, titled Is Justified True Belief Knowledge?, Gettier showed, by means of two counterexamples, that there were cases where individuals had justified true belief of a claim, but still failed to know it. Thus, Gettier showed that the JTB account was inadequate-- it could not account for all of knowledge. The JTB account was first credited to Plato, though Plato argued against this very account of knowledge in the Theaetetus (210a).