Fermilab’s Conventional Facilities Group worked with the Linear Collider Forum of America to initiate an industrial study to verify costs for underground construction. Unit costs for underground construction had been developed initially through a combination of in-house experience and supporting consultant input. This study would provide an independent “second opinion” based only on the experience of the newly selected consulting firm, with the benefit of previously collected data. This unit costs requested would be based on specifically defined underground construction activities required by the ILC Project including: cost per unit length of excavated tunnel for various tunnel diameters using tunnel boring machines, shaft construction, general underground excavation, tunnel invert installation, cross tunnel penetrations and personnel access enclosures. In an effort to maintain global consistency, the definitions for underground construction activities and respective unit costs were also used in consulting agreements developed in the European and Asian Regions for similar unit costs.