条件概率分布（Conditional Probability Distribution，或者 条件分布，Conditional Distribution ）是现代概率论中的概念。已知两个相关的随机变量X 和Y，随机变量Y 在条件{X =x}下的条件概率分布是指当已知X 的取值为某个特定值x之时，Y 的概率分布。 如果Y 在条件{X =x}下的条件概率分布是连续分布，那幺其密度函数称作Y 在条件{X =x}下的条件概率密度函数（条件分布密度、条件密度函数）。与条件分布有关的概念，常常以“条件”作为前缀，如条件期望、条件方差等等。

In probability theory and statistics, given two jointly distributed random variables X and Y, the conditional probability distribution of Y given X is the probability distribution of Y when X is known to be a particular value; in some cases the conditional probabilities may be expressed as functions containing the unspecified value x of X as a parameter. In case that both "X" and "Y" are categorical variables, a conditional probability table is typically used to represent the conditional probability. The conditional distribution contrasts with the marginal distribution of a random variable, which is its distribution without reference to the value of the other variable.