Johann Karl Wilhelm Illiger (November 19, 1775 - May 1813) was a German entomologist.

Illiger was the son of a merchant in Brunswick. He studied under the entomologist Johann Hellwig, and later worked on the zoological collections of Johann Centurius Hoffmannsegg. Illiger was professor and director of the zoological museum in Berlin from its formation in 1810 until his death.

Illiger was the author of Prodromus systematis mammalium et avium (1811), which was an overhaul of the Linnean system. It was a major influence on the adoption of the concept of the 'Family'.

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