经典条件反射（巴夫洛夫制约、反应制约、alpha制约），又译古典制约，是一种关联性学习。这种产生制约行为的学习型态被伊凡·彼得罗维奇·巴夫洛夫描述为动物对特定制约刺激的反应。最简单的形式，是亚里斯多德曾经提出的接近律，也就是当两件事物经常同时出现时，大脑对其中一件事物的记忆会附带另外一件事物。

古典制约理论一开始的重点放在反射行为或是非自愿行为。任何一个反射都是中性刺激与产生的反应两者的关系。近几年来对古典制约理论所做的反射限制被抛弃，且自愿行为的制约刺激也成为重要研究。

Classical conditioning (also known as Pavlovian or respondent conditioning) is a learning process in which an innate response to a potent stimulus comes to be elicited in response to a previously neutral stimulus; this is achieved by repeated pairings of the neutral stimulus with the potent stimulus. The basic facts about classical conditioning were discovered by Ivan Pavlov through his famous experiments with dogs. Together with operant conditioning, classical conditioning became the foundation of behaviorism, a school of psychology which was dominant in the mid-20th century and is still an important influence on the practice of psychological therapy and the study of animal behaviour (ethology). Classical conditioning is now the best understood of the basic learning processes, and its neural substrates are beginning to be understood.