兰科（学名：Orchidaceae）植物俗称兰花，亦叫胡姬花，是开花植物中最大、最具多样性的科，约有736属和28,000种，和另外100,000余个园艺家培养的交配种和变种。所有的野生兰科植物均被列为《野生动植物濒危物种国际贸易公约》(CITES)的保护范围。

早期的分类系统（克朗奎斯特分类法）将兰科与水玉簪科分类于微子目内，在1998年发表的APG 分类法中归于仙茅目中，而2003年经过改进的以基因亲缘关系分类的APG II 分类法则将其列于天门冬目下，并认为与仙茅科亲缘关系接近。

兰花由于植物区系的极度复杂性，花的所有特征都充分表现对昆虫授粉的高度适应性，并与真菌创建共生关系，被认为是植物演化的顶点。

The Orchidaceae are a diverse and widespread family of flowering plants, with blooms that are often colourful and often fragrant, commonly known as the orchid family. Along with the Asteraceae, they are one of the two largest families of flowering plants. The Orchidaceae have about 27,800 currently accepted species, distributed in about 880 genera. The determination of which family is larger is still under debate, because verified data on the members of such enormous families are continually in flux. Regardless, the number of orchid species nearly equals the number of bony fishes and is more than twice the number of bird species, and about four times the number of mammal species. The family also encompasses about 6–11% of all seed plants. The largest genera are Bulbophyllum (2,000 species), Epidendrum (1,500 species), Dendrobium (1,400 species) and Pleurothallis (1,000 species).