Information regarding arrivals in Pisa.
Arrival from within Europe (short haul flights): Pisa is served by an international airport with flights from many European cities. The airport is located roughly 30 minutes by foot from the city center. The city center can also be reached by taxi (typically 15-20 euros), and the "Pisa Mover", which however only covers half the distance to the city center, for around 5 euros, and drops you off at the train station.
Alternatively, your plane may arrive at Florence airport from where you can commute to the Santa Maria Novella train station via Tram and then take a 1-hour regional train to Pisa, see instructions below. You may also arrive at Bologna airport, which is a bit further away, see again instructions for trains below.
Arrival from outside Europe (long haul flights): Assuming you arrive in Italy via a long haul flight, you will most likely land in Rome or Milan. From there you can take a long distance train to Pisa (Frecciarossa, Frecciargento, Frecciabianca by Trenitalia, or alternatively by an Italo train). These are high speed trains, whose ticket prices fluctuate based on demand and other parameters. Hence, these should be pre-booked for the lowest prices. The Pisa railway station "Pisa Centrale" is located 15 minutes by foot from the city center.
Arrival from within Europe (long distance trains): See the above paragraph.
Arrival from within Europe (short distance trains): You may also arrive via a regional (short distance) train, called "Regionale" or "Regionale Veloce". For these tickets, the prices are fixed, and do not fluctuate based on demand. Thus these are easily obtained from ticket machines or counters immediately upon your arrival in the train station.