Regardless of how long you might be planning to stay and travel around in Australia, all visitors are required by law to obtain a visa, and there are different types of visas available that covers tourism, study, work and permeant residency visas. Tourist visas can be obtained online with minimal hassle, and only take a few days to be processed. Give yourself at least one or two weeks when getting the visa, just to be on the safe side. Citizens of Canada and the UK do not need to apply for visas. However, they will need to apply online and receive electronic travel authorization before going. US citizens can obtain a visa online which will be valid for up to three months.