关键设施原理（或译为枢纽设施原理）是一种在竞争法下产生的独占行为的一种特别型态。一般来说，它是指一家拥有市场力的公司在市场中使用瓶颈来阻断竞争者进入该市场的反竞争行为。某种程度接近拒绝交易的涵义。

一般以美国反托辣斯法中所陈述的四个要件来说明关键设施：

对于潜在的反竞争者来说，要以这些要件归咎是相当困难的。而对对于反竞争者来说，何谓在明显的市场下的「关键」设施呢？而哪些设施某种程度是对于竞争是有必要的，并且会让小公司无法与市场领导者竞争呢？同样的，有哪些设施可让主导公司允许其他人使用，而不会阻碍其主导服务顾客的地位呢？

The essential facilities doctrine (sometimes also referred to as the essential facility doctrine) is a legal doctrine which describes a particular type of claim of monopolization made under competition laws. In general, it refers to a type of anti-competitive behavior in which a firm with market power uses a "bottleneck" in a market to deny competitors entry into the market. It is closely related to a claim for refusal to deal.