If you arrive in Venice by plane, the Marco Polo airport (at Tessera, Venezia) is only 13 km far from Venice. You can choose to take a taxi, a urban bus, a shuttle or a waterbus.
by taxi: to Venice – Piazzale Roma, travel time: 10 minutes; cost: 40 Euro
taxi

by urban bus (ACTV line 5): to Venice – Piazzale Roma; travel time: 23 minutes; cost: 8 Euro
by shuttle bus (ATVO shuttle): to venice-Piazzale Roma; travel time: 20 minutes; cost: 8 Euro
bus

by waterbus Alilaguna
Three lines take you in different parts of the town.
Alilaguna

If you arrive in Venice by train, you can check here.
The train station is named Venezia Santa Lucia, not to be confused with Venezia Mestre.

From Mestre to Venice

If you arrive or stay in Mestre, in the mainland, you can reach Venice by train, by bus or by taxi.

The best and cheapest way to reach Venice is by train: Venice Mestre – Venice Santa Lucia; travel time: 10 minutes; cost: 1-1.30 Euro (depending on train).
Check the timetables here.

By urban bus: from Mestre to Venice Piazzale Roma; travel time: 15 minutes; cost: 1,50 Euro.
Check the lines and timetables here.
By taxi: from Mestre to Venice Piazzale Roma; travel time: 10 minutes; cost: 23 Euro.
radiotaxivenezia