Interest can represent an important portion of the award depending on the time between the origin of the claim and the actual payment of compensation or damages. It can sometimes even exceed the principal. This chapter discusses the three most important issues with regard to the determination of interest: 1) the rate of interest, 2) the period of interest, and 3) the question of whether interest should be compounded. A differentiation between ‘pre-award interest’ and ‘post-award interest’ seems advisable as the former represents an item of compensation or damages, while the latter could be regarded as default charges for the non-payment of a debt. Post-award interest should additionally encourage prompt compliance with the award.