OV-chipkaart
To make getting around Delft and the Netherlands as easy as possible, you should get a plastic public transport card, or OV-chipkaart. This card allows you to use buses, trains and trams throughout the country with a digital payment system. With it, you can scan in and out of a railway station, bus or tram. As you use the card, you will occasionally need to top it up; this can be done online and at transfer points.
There are two types of OV-chipkaarts. First, the personalised OV-chipkaart. It is valid for 5 years and allows you to buy products and discounts for railway travel. If you are planning to use the trains frequently, it is worth looking into the options available for the personalised OV-chipkaart, for example, free travel on weekends and discounted travel in off-peak times. Information on products can be found here. You can order a personalised OV-chipkaart online (see link below) or by post. Second, you can get an anonymous card. This card can be shared among any number of people. It can only be used by 1 person at a time, however. You cannot use it to buy train discount packages. You can buy an anonymous card at a railway station.
You will see yellow self-service machines at railway stations. At these terminals, you can check your balance and top up your OV-chipkaart. They all have an English language feature. It is possible to buy individual tickets each time you travel, but this is a little bit more expensive. If you intend to travel frequently, an OV-chipkaart will be cheaper and more convenient. For more information have a look at the OV-chipkaart website. (All information on the website is also available in English.)