需求曲线是显示在特定时间内，某物品的价格与需求量关系的曲线，反映了需求表两个矢量的线性关系。

需求曲线是需求表和需求函数的图像化表达， 并且和供给表或供给函数交接组成均衡点，用以表示市场上生产者和需求者能够构成交易的物品数量和价格。 需求曲线既可以以“曲线”出现，也可以使用“直线”方式出现。理论上，可以符合需求定理的需求曲线只可以是向右下倾斜的，所以韦伯伦商品和吉芬物品便是泛指那些需求曲线并非从左到右倾斜的物品。 作为微观经济学的基本原理，需求曲线相关理论自从19世纪末秉承边际效用理论而发展成主观的价值理论，并用价格解释物品价值，其核心思想从未修改。

In economics, the demand curve is the graph depicting the relationship between the price of a certain commodity and the amount of it that consumers are willing and able to purchase at that given price. It is a graphic representation of a demand schedule. The demand curve for all consumers together follows from the demand curve of every individual consumer: the individual demands at each price are added together.