在可计算性理论与计算复杂性理论中，所谓的决定性问题（Decision problem）是一个在某些形式系统回答是或否的问题。例如：「给两个数字x与y，x是否可以整除y？」便是决定性问题，此问题可回答是或否，且依据其x与y的值。

决定性问题与功能性问题（Function problem，或复杂型问题）密切相关，功能性问题的答案内容，较简单的是与非复杂许多。范例问题：「给予一个正整数x，则哪些数可整除x？」

另一个与上述两类问题相关的是最佳化问题（Optimization problem），此问题关心的是寻找特定问题的最佳答案。

In computability theory and computational complexity theory, a decision problem is a question in some formal system with a yes-or-no answer, depending on the values of some input parameters. Decision problems typically appear in mathematical questions of decidability, that is, the question of the existence of an effective method to determine the existence of some object or its membership in a set; some of the most important problems in mathematics are undecidable.