Most travelers connecting through Heydar Aliyev International Airport without leaving the secure transit area do not need a visa of any kind, provided their layover stays within the airport's international transit zone and connecting flights are same-day or next-day. If you want to leave the airport during a longer layover — for example, to see Baku's Old City on a 24+ hour stopover — you'll need either the standard eVisa or, in some cases, a dedicated transit visa depending on your nationality and onward itinerary.
If your layover is 12+ hours, applying for the standard eVisa (rather than a separate transit visa) and spending the time exploring the Old City and Boulevard is genuinely worthwhile — Baku is one of the more rewarding stopover cities in the region. See our 2-day Baku itinerary for how we'd structure a short visit, or contact us directly for a layover-specific plan.