表型（英语：Phenotype），又称表现型，对于一个生物而言，表示它某一特定的物理外观或成分。一个人是否有耳珠、植物的高度、人的血型、蛾的颜色等等，都是表型的例子。

表型主要受生物的基因型和环境影响，表型可分为连续变异或不连续变异的。前者较易受环境因素影响，基因型上则会受多个等位基因影响，如体重、智力和身高；后者仅受几个等位基因影响，而且很少会被环境改变，如血型、眼睛颜色和卷舌的能力。对于不连续变异，若有两个生物表现型相同，其基因型未必一样，这是因为其中一方可能有隐性基因。

表型变异是进化论物竞天择理论成立的重要条件。早期的遗传学家欠缺分子生物学技术，无从直接观察DNA构造，生物和其后代的表型就是他们判别其基因型的工具。

A phenotype (fromGreek phainein, meaning "to show",and typos, meaning "type") is the composite of an organism's observable characteristics or traits, such as its morphology, development, biochemical or physiological properties, phenology, behavior, and products of behavior (such as a bird's nest). A phenotype results from the expression of an organism's genes as well as the influence of environmental factors and the interactions between the two. When two or more clearly different phenotypes exist in the same population of a species, the species is called polymorph.