Encyclopedias, Almanacs, Transcripts, and Maps
- Wren–warblers
- Wriedt, Etta (ca. 1859-1942)
- Writing Preserves Knowledge and Memory
- Wu Xien (Wu Hsien)
- Wu, Chien-Shiung
- X rays
- X Rays
- X-linked hydrocephaly
- X-Linked Hydrocephaly
- X-Linked Mental Retardation
- Xavier, Francisco Candido (1910-)
- Xenocrates of Chalcedon
- Xenogamy
- Xenogamy
- Xenoglossy
- Xeroderma pigmentosum
- Xeroderma Pigmentosum
- Xerox Introduces the First Photocopier
- XX male syndrome
- XX Male Syndrome