Impact investments have gained tremendous recognition among investors as well as policy makers in the last years. However, specific details about impact investments are not well understood yet. Specifically, academic research about the magnitude, life cycle, and tradeoffs of impact is still in its infancy. This paper provides practical guidance by developing principles for critical topics of impact measurement, assessment, and valuation using an exploratory approach. Questions that will be tackled include, among others: What is a significant positive company impact (impact magnitude)? Can impacts be transferred between investors (impact life cycle)? How should tradeoffs between impact categories be handled (impact tradeoffs)? The paper proposes 16 principles that provide answers to these and other questions, illustrates their real-world significance through case studies, and provides a discussion of their implications and limitations. It is, however, only one step and much more work is required to standardize the measurement, assessment, and valuation of impact in impact investments. Overall, this paper suggests important steps for this standardization process.