Lygodactylus williamsi is a critically endangered species of lizard in the family Gekkonidae. The species is endemic to a small area of Tanzania. Common names include turquoise dwarf gecko, William's dwarf gecko and, in the pet trade, electric blue gecko or electric blue day gecko.

Illegally wild-caught specimens are widely sold in the pet trade, often falsely promoted as captive-bred. Although L. williamsi breeds in captivity, the young require a lot of specific care, making large-scale breeding difficult. There is some specialist breeding, with one very large breeder claiming to have produced about a thousand individuals as of 2017, but no large-scale professional breeding. A captive breeding project and studbook was initiated by EAZA-registered zoos in 2013.

L. williamsi, as a species, was placed under EU Appendix B protection (December 2014) and EU Appendix A protection (January 2017), and given CITES Appendix I protection in January 2017, as well. The gecko may not be kept or sold in the EU without documentation and permits, renewable every three years, and geckos must now be registered. Similar restrictions apply in many other jurisdictions.

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