To/from Marco Polo Airport:

Bus
Regular express buses travel between Venice Marco Polo and Venice (Piazzale Roma) and Venice Mestre (Train Station), one-way €6, return €11.

Local buses also connect Venice/Mestre and the airport.

Alilaguna (Waterbus)
Two Alilaguna waterbuses connect the airport with various stations on Venice and its islands, including the cruise port. Airport transfers on the Alilaguna cost €15 one-way and €27 return. Passes valid for 72 hours are also available. A third Alilaguna line connects Venice with Murano and the company also runs Canal Grande tours. Note Alilaguna services are provided by a different company to the Vaporetto and separate tickets are required for each service.

Water taxi
Water taxis offer exclusive airport transfer in true Venetian style.
Various companies run water taxi services.
Private water taxi airport transfer start from €95 one-way for up to four people. Shared transfers are also available for €25 per person.

Taxis
Regular four-wheeled, land-based taxis are also of course in plentiful supply directly outside the arrivals gate, and you can expect to pay at least €35-40 for the trip to Piazzale Roma in Venice proper.


To/from Treviso Canova Airport:

Bus
Two providers offer express bus connections between Treviso airport and Venice/Venice Mestre (Train station).

Borzi - about 40 minutes
One way ticket €10. Return (valid 10 days) €18.
http://en.barziservice.com/

Atvo - about 70 minutes
One way ticket €10. Return (valid 10 days) €18.

A local bus connects the airport with Treviso (town centre) and the train station. Purchase your tickets before boarding the bus, tickets available from stand inside the terminal or from cafés, tobacconists and newsstands all around Treviso.

Train
The Treviso train station is located on the edge of the town centre, a few kilometres from the airport - take the local bus or a taxi to get to/from the airport. Trains depart regularly to Venice and Venice Mestre (from €2.90, 30-40 minutes).