Mastigophora, phylum of unicellular heterotrophic protozoans of the kingdom Protista. Most of the approximately 1,500 species of Mastigophora are propelled by one or more flagella, and members of the group are sometimes referred to as flagellates. Some have pseudopodia, temporary armlike protrusions of cytoplasm that help the cell move about and enwrap particles of food. Asexual reproduction by binary fission is the norm, but some species reproduce sexually by a process called syngamy, the fusion of two gametes produced by meiosis (i.e., fertilization).

Some parasitic members of the Mastigophora are the causative organisms of disease in humans and other animals. Trypanosomes, for example, are the cause of African sleeping sickness and Chagas' disease, and giardiasis is caused by the mastigophoran Giardia lamblia.

See Sarcomastigophora