[en] The DIT code is the ABB Combustion Engineering nuclear fuel assembly pressurized water reactor (PWR) design code developed in the early 1970s and used for licensing calculations since 1978. From its beginning, DIT has been based on integral transport theory combined with the interface current method. The name DIT was chosen to acknowledge that within open-quotes cells,close quotes one option for calculating collision probabilities was the discrete integral transport method developed by Carlvik. This paper reviews the transport methods used in DIT and the ways in which they have been applied. Advantages and limitations are discussed, and some recently developed applications are described