变形虫门是一类似变形虫的（amoeboid）原生生物。变形虫门的多数物种靠细胞内原生质的流动而移动。伪足类似于手指形状、边缘是钝的，所以称作lobopodia，直译为钝的伪足. 大多数是单细胞生物。在土壤中或水域中生存。某些也被发现与其它生物共生，某些甚至是病原体。变形虫门还包括黏菌（slime moulds）, 这是多核或多细胞生物，具有变形虫的形态，但又类似于真菌可以产生孢子，通常肉眼可见。

变形虫门生物的尺寸变化很大。许多仅10-20 μm，但也有很大尺寸的原生生物品种，如著名的大变形虫（Amoeba proteus），达到800 μm长，并且由于它的可观的尺寸成为了用于研究的有代表性的细胞。多核变形虫，如卓变形虫属（Genus Chaos）与多核变形虫属（Genus Pelomyxa）可达数毫米长，而某些黏菌面积可达数平方英尺（接近1平方米）。

Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In most classification schemes, Amoebozoa is ranked as a phylum within either the kingdom Protista or the kingdom Protozoa. In the classification favored by the International Society of Protistologists, it is retained as an unranked "supergroup" within Eukaryota. Molecular genetic analysis supports Amoebozoa as a monophyletic clade. Most phylogenetic trees identify it as the sister group to Opisthokonta, another major clade which contains both Fungi and Animals as well as some 300 species of unicellular protists. Amoebozoa and Opisthokonta are sometimes grouped together in a high-level taxon, variously named Unikonta, Amorphea or Opimoda.