优选理论(Optimality Theory，简称OT)或最适性理论，是一种语言学模型，该理论认为语言表面可见的形式源自数个互相冲突的限制(constraints)之间的相互作用。优选理论不同于其他音韵分析方法，像是自动段音韵学(Autosegmental phonology)及线性音韵学(SPE)等理论通常以规则(rules)描述而非限制(constraints)。优选理论将语法规则(grammars)模型化为一系统，此系统提供从输入到输出的映射(mapping)；基本上，输入被视为底层结构(Underlying representation)，而输出则是表层结构(surface representation)。

Optimality Theory (frequently abbreviated OT; second word normally capitalized by convention) is a linguistic model proposing that the observed forms of language arise from the interaction between conflicting constraints. OT differs from other approaches to phonological analysis, such as autosegmental phonology and linear phonology (SPE), which typically use rules rather than constraints. OT models grammars as systems that provide mappings from inputs to outputs; typically, the inputs are conceived of as underlying representations, and the outputs as their surface realizations.