AphID includes a key to the 66 most polyphagous and cosmopolitan aphid species. The key for slide-mounted specimens has 132 end points. The key does not include males, oviparae, or immatures. It may not work for all fundatrices or alatae and apterae from primary hosts (for those species with host alternation). AphID includes all 38 aphid species in the dichotomous keys to polyphagous aphids in the three seminal works by Roger Blackman & Victor Eastop (1994, 2000, 2006). The remaining aphids represent the 28 species most frequently intercepted at United States ports of entry that are not already represented on the Blackman & Eastop list. AphID offers users detailed descriptions of morphological features critical to identifying aphids along with annotated photographs to help illustrate each feature. Separate pages are devoted to suites of features, for example all features of the antenna are found on the same page. The morphology pages are crosslinked with a detailed glossary.