镅（Americium，港台译作“镅”）是一种放射性超铀元素，符号为Am，原子序为95。镅属于锕系元素，在元素周期表中位于镧系元素铕之下。镅是以发现所在的美洲大陆（America）命名的。

位于伯克利加州大学由格伦·西奥多·西博格领导的团队在1944年首次合成了镅元素。虽然镅是第三个超铀元素，但它却是继锔以后第四个被发现的超铀元素。这项发现最初被列为机密，直到1945年才公诸于世。大部分的镅都是在核反应炉中以中子撞击铀或钚而形成的：一吨乏核燃料含有大约100克镅。镅元素主要用在商业电离室烟雾探测器和仪表中，或用作中子源。有人提出用Am同位素制造核电池和太空船的核推进燃料，但因该同核异构体的稀少和昂贵而尚待实现。

Americium is a radioactive transuranic chemical element with symbol Am and atomic number 95. This member of the actinide series is located in the periodic table under the lanthanide element europium, and thus by analogy was named after the Americas.

Americium was first produced in 1944 by the group of Glenn T. Seaborg from Berkeley, California, at the metallurgical laboratory of University of Chicago. Although it is the third element in the transuranic series, it was discovered fourth, after the heavier curium. The discovery was kept secret and only released to the public in November 1945. Most americium is produced by uranium or plutonium being bombarded with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains about 100 grams of americium. It is widely used in commercial ionization chamber smoke detectors, as well as in neutron sources and industrial gauges. Several unusual applications, such as a nuclear battery or fuel for space ships with nuclear propulsion, have been proposed for the isotope Am, but they are as yet hindered by the scarcity and high price of this nuclear isomer.