Aedes aegypti and Aedes albopictus have the potential to transmit several viruses, including dengue, chikungunya, Zika, and yellow fever. None of these viruses are currently known to be transmitted within California, but thousands of people are infected with these viruses in other parts of the world, including in Mexico, Central and South America, the Caribbean, and Asia. The presence of Aedes aegypti and Aedes albopictus mosquitoes in California poses a threat that Zika, dengue, and chikungunya viruses can be transmitted in infested areas from returned infected travelers. Travelers can protect themselves by preventing mosquito bites. When traveling to countries with dengue, chikungunya, or Zika, use insect repellent, wear long sleeves and pants, and stay in places with air conditioning or with window and door screens.