生物分类学通常直接称分类学（英语：taxonomy），是一门研究生物类群间的异同以及异同程度，阐明生物间的亲缘关系、进化过程和发展规律的科学。要将生物分类，首先要知道生物与非生物的定义，但是我们似乎没有办法准确定义，以病毒来说，虽然可在其他生物体内寄生并复制，但在生物体外却没有一般生物的特征如制造或摄取营养，生殖等现象。又如引起疯牛病的朊粒（prion）可以造成感染却无DNA成分，一直以来，DNA被视为生命遗传物质，经由与RNA的转录转译过程，形成蛋白质，再进一步形成组成细胞的各个部分，如细胞膜、胞器等，而细胞则是我们长久以来所认为组成生命体的最小单位。

Taxonomy (from Ancient Greek: τάξις taxis, "arrangement", and -νομία -nomia, "method") is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. Organisms are grouped together into taxa (singular: taxon) and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a super group of higher rank, thus creating a taxonomic hierarchy. The Swedish botanist Carl Linnaeus is regarded as the father of taxonomy, as he developed a system known as Linnaean classification for categorization of organisms and binomial nomenclature for naming organisms.