One of the classic ingredients for a Belgian Wit. Use 1/2 to 1oz  coarsely ground seed (depending on your taste)
for each 5 gallons you are brewing. Add the ground seed anywhere from 20 minutes to the end of the boil (right
before chilling). Flavor intensity can be varied by amount used, coarseness of grind and amount of time in the boil.
If you are making a Wit, you may also want to add Bitter Orange Peel (also 1/2 to 1 oz by taste per 5 gallons).