Transport in Japan works slightly differently than it does in Australia and most parts of the West. Instead of having a train ticket that covers a certain period of travel (ah, the good ol’ 2-hour tickets of my youth…) you pay for the distance that you travel. Which can seem expensive, when you consider that to travel just one station away, it can cost upwards of 130 yen.
When you use the trains here, you will buy a ticket from the vending machines, insert it into the gate to let you in, take the ticket again, then, once you have reached your destination, insert the ticket into the gate you want to exit. Assuming you’ve paid the correct fare, the ticket will be swallowed up by the machine and you carry on your way.
Buying a ticket at every train station can be tedious though, so it’s much easier to have a prepaid card that simply deducts the amount you have travelled, until you have run out of credit. Like phonecards, these usually have collectable designs on them but when the credit runs out, it runs out – and the cards become useless.
In Tokyo, though, JR (Japan Railways) have gone one better with the Suica card system. Suica stands for “Super Urban Intelligent CArd” but the word also means “watermelon” in Japanese. It’s a hard plastic card, like a credit card, and can be topped up with more credit at the ticket machines, so that means less paper wastage from tickets and prepaid cards.
The cards can be bought for 2000 yen (including a 500 yen deposit on the card) at most train stations in metropolitan Tokyo. They work using RFID (radio frequency identification) technology developed by Sony. The cards do not need to be placed into a slot, but rather just pressed against a sensor plate. The excellent thing about this technology is that the RFID signal can be read through other cards and layers, so in fact, all you need to do is press your wallet against the plate, and the card inside will be read.
The Suica card is incredibly convenient for those reasons, but best of all – you can use the Suica card to pay for items in many shops inside train stations. Look out for the Suica penguin logo outside the shop – whether it’s a combini or a ramen bar – and you can scan your card for all your purchases. Useful, if you’ve run out of change or if the ATM isn’t open.
The Suica card is available to use on all JR East lines, the Tokyo Monorail and the Tokyo Waterfront Railway (also known as the Rinkai Line). In the future, Suica will be adapted for use by train lines that use the Passnet system, which basically means you can get almost anywhere around Tokyo on your Suica. And get a drink from the kiosk, too.

Links:
Wikipedia
JR East (English)