Interface engineering is part of the detailed engineering of plant design when two or more engineering, procurement and construction (EPC) contractors are involved. It deals with the exchange of design, schedule and construction details between all contracting parties.

In the past, a large plant used to be built by one EPC contractor. Today, installations are being put up in a much bigger scale to make it more cost-effective. The time frame from when the investment decision has been made to commissioning is also getting shorter. To avoid any schedule or budget overrun risk, the owner may divide the whole complex into several smaller contracts implemented by multiple EPC contractors. The timely and accurate exchange of design, schedule and construction information between design offices becomes important. This exchange of information is to minimize rework at a later date and avoid last-minute surprises during commissioning.