If you are a U.S. citizen, you must have a valid U.S. passport and a visa or an approved Electronic Travel Authority (ETA) to enter Australia. Most U.S. passport holders traveling to Australia for tourism or business purposes for less than 90 days can obtain an ETA, which is an electronic label-free visa and can be obtained at the ETA website for a small service fee. There are different Australian visa types available for travelers to Australia, and knowing which Australian visa to apply for depends on the length of your stay, your passport, and the purpose of your visit. Here are some of the most common visa types:

• Electronic Travel Authority visa (subclass 601): This visa allows you to visit Australia as many times as you want, for up to a year, and stay for three months each visit. This visa is available to passport holders from a number of countries and regions, who live outside Australia. A step-by-step guide on how to apply is available on the ETA website.

• eVisitor (subclass 651): This is a free visa for multiple visits to Australia for tourism or business purposes for up to three months at a time within a 12-month period. This visa is available to passport holders from a number of European countries and cannot be extended.

• Visitor visa (subclass 600): The Visitor visa allows you to visit Australia, either for tourism or business purposes. It is open to all nationalities. Generally, a period of stay of up to three months is granted, but up to 12 months may be granted in certain circumstances.

Please note that depending on the type of visa you apply for, the length of your stay, and your intended activities in Australia, you may be required to undergo a medical examination before the Australian Department of Home Affairs will issue you a visa. It is recommended to verify the visa information with the Embassy of Australia in Washington D.C. before you travel.