Pisa has regular trains to and from Florence (usually three per hour), to and from Lucca (usually every hour) and is also accessible by bus, and has an international airport.
Pisa Centrale is the main train station of Pisa. Rome to Genova trains stop at Pisa Centrale. If you are planning an in-route visit to Pisa, it is also convenient since Pisa Centrale has Left Luggage service open from 6AM-9PM. Each baggage deposited costs €3 for 12 hr. Else, if you are in the city just to see the Leaning Tower, you could also get down at the Pisa S. Rossore train station which is much closer to the Tower. Do check the train schedule as not all trains would stop there. However there are regional trains to Florence every hour at the 46th minute (as on 9th July 2012).
Pisa Galileo Galilei Airport (IATA: PSA) is the main airport of Tuscany and is served by several airlines operating hundreds of weekly flights to national and international destinations. Numerous companies offer charter flights to and from a number of European and non-European destinations. Flying to Pisa is really cheap and easy: the most recognized low-cost airlines serve Pisa. The airport is close to the city center - it takes only a few minutes to reach the center by bus, train or taxi. The airport is also within easy walking distance of the center, which takes around 20 min.
Do not expect the airport to be open 24/7, though. Many smaller European airports do have opening hours, so don't expect to stay overnight or hang out until late.
You can purchase bus and train tickets from the information desk in the arrivals hall. The trains are the fastest way to get to the city but run only twice per hour. The tickets cost €1.10 and the ride takes only about 5 min.
The bus (The Red Line or LAM Rosso towards Jacobo) has a regular service every 15 min and it takes about 15 min to get to the city. The bus runs to Piazza dei Miracoli and the central station. Since the ticket
