青霉菌是最常见的真菌（半知菌）中的一种。肉眼可见其孢子的颜色为蓝绿色，因而得名。但是并非所有青霉属的霉菌都为蓝绿色，也有白色或者绿色。在显微镜下，可见其呈笔一样形状的笔状体（penicillus）构造，尖端上带有孢子。这也就是这种霉菌的学名由来。

1928年英国生物化学家弗莱明在实验室中发现特异青霉菌（P. notatum）具有杀菌作用；1938年由恩斯特·伯利斯·柴恩（Earnest Chain, 1906-1979）、弗洛里（Howard Florey, 1898-1968）及希特利（Norman Heatley, 1911-2004）领导的团队提炼出青霉素，从而改变了人类与传染病之间生死搏斗的历史。

Penicillium (/ˌpɛnɪˈsɪlɪəm/) is a genus of ascomycetous fungi of major importance in the natural environment as well as food and drug production.

Some members of the genus produce penicillin, a molecule that is used as an antibiotic, which kills or stops the growth of certain kinds of bacteria inside the body. Other species are used in cheesemaking. According to the Dictionary of the Fungi (10th edition, 2008), the widespread genus contains over 300 species.