Azerbaijan Airlines and Qatar Airways fly from Baku to Tbilisi 3 times a day. Alternatively, Azerbaijan Railways (ADDY) operates a train from Baku to Tbilisi once daily. Tickets cost $6 - $35 and the journey takes 12 h 40 min.
How to get from Baku to Tbilisi
From Central station Aeroexpress to Baku airport, fly to Tbilisi airport, then line 37 bus to Tbilisi. 4 h 50 min $77. From Keshlya train to Tbilisi station. 12 h 40 min $9. From Baku drive to Tbilisi. 7 h 14 min $56.