Alien species, also known as invasive species, are organisms that are introduced to a new environment where they do not naturally occur. These species can be plants, animals, or microorganisms that often disrupt local ecosystems, outcompeting native species for resources and altering habitats. The introduction of alien species can happen through various means, such as global trade, travel, or accidental transport. Some well-known examples include the Burmese python in the Florida Everglades and the zebra mussel in the Great Lakes. Managing these species is crucial to protect biodiversity and maintain ecological balance.