贝氏网络（Bayesian network），又称信念网络（belief network）或是有向非循环图形模型（directed acyclic graphical model），是一种机率图型模型，借由有向非循环图形（directed acyclic graphs, or DAGs）中得知一组随机变量{}及其n组条件机率分配（conditional probability distributions, or CPDs）的性质。举例而言，贝氏网络可用来表示疾病和其相关症状间的机率关系；倘若已知某种症状下，贝氏网络就可用来计算各种可能罹患疾病之发生机率。

A Bayesian network, Bayes network, belief network, Bayes(ian) model or probabilistic directed acyclic graphical model is a probabilistic graphical model (a type of statistical model) that represents a set of random variables and their conditional dependencies via a directed acyclic graph (DAG). For example, a Bayesian network could represent the probabilistic relationships between diseases and symptoms. Given symptoms, the network can be used to compute the probabilities of the presence of various diseases.