Technological distance has been a widely used concept since the seminal paper on R&D spillovers by Jaffe in 1986. Scholars in the field of M&A, alliances and R&D spillovers have used the concept of technological distance in their research. In this dissertation, the author provides a discussion of the concept of technological distance and the statistical properties of distance measures. Three new measures are introduced to the literature. These measures as well as seven existing measures are assessed axiomatically and empirically. Furthermore, the author assesses the role of technological distance in the target choice decision and the level of the transaction price in M&A transactions.