Many tourists agree that the best time of year to visit Delft is in the spring or summer. Visiting in the fall is also nice, but you miss out on the longer days and some of the better festivals that take place in the warmer months. If you visit in the spring or summer, you get to take part in many Dutch customs and festivals. You also get a chance to see the true beauty of the Dutch countryside. If you visit during the fall you will still get to see some of these aspects of Dutch life, but on a smaller scale. Visiting in the winter is also possible, but you will have to deal with snow and colder temperatures. If you don't mind the colder weather then it isn't really a problem, but you won't be able to do as many things outdoors. A lof of people come to Delft because they like participating in the outdoor activities, and those are unavailable in the winter. If you come to Delft in the spring or summer, you should pack clothes that will keep you comfortable. Shorts, t-shirts, and anything else that will allow you to enjoy your time here is a good idea. You should also have a pair of pants and a light jacket for the night time, as the temperatures can dip quite a bit.