Visas are required by all except visitors from Belarus, China, Georgia, Iran, Kazakhstan, Kyrgyzstan, Moldova, Mongolia, Russia, Tajikistan, Turkey, Ukraine and Uzbekistan.
When applying for a visa you may need an invitation. Rules vary depending on where you apply and are far from straightforward. Visas are valid for up to 90 days.
In some cases it is a lot cheaper (US$20) to apply for a tourist visa than an entry visa (US$150).
Visa information
Azerbaijan embassies and consulates - use links at the bottom of the page