绿藻门是绿藻中的一门，包含有约8000个物种，大部份都是水生光合真核生物。和陆生植物 （苔藓植物和维管植物）一样，绿藻也含有叶绿素 a 和 c ，且将能源转化为淀粉存在其色素体内。绿藻门和轮藻门与有胚植物相关，一起合称为植物。

此门包含单细胞和多细胞的物种。大部份物种生活在淡水里，其他许多物种则居住在海水中，另外还有一些物种适应了许多的环境，如雪藻居住在夏天的高山雪原中。其他还有依附在岩石或树木上头的。一些地衣和真菌与绿藻有共生关系，绿藻门中的藻类也会和原生动物、海绵及刺胞动物等形成共生关系。有些会有鞭毛而利于移动，有些会行同配生殖或异配生殖等有性生殖。

Chlorophyta is a division of green algae, informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a highly paraphyletic group of all the green algae within the green plants (Viridiplantae) and thus includes about 7,000 species of mostly aquatic photosynthetic eukaryotic organisms. In newer classifications, it refers to one of the two clades making up the Viridiplantae, which are the chlorophytes and the streptophytes. The clade Streptophyta consists of two divisions, the Charophyta and the Embryophyta. In this sense the Chlorophyta includes only about 4,300 species. Like the land plants (bryophytes and tracheophytes), green algae contain chlorophyll a and chlorophyll b and store food as starch in their plastids.