Increasingly complex supplier-relationships dominate product development, independent of industries and products. Mostly the primary source of risks and later problems is insufficient coherence with requirements engineering methodology and collaboration between different business partners during the project. This article based on experiences from various industries and projects provides insight into how to effectively collaborate in requirements engineering. The Requirements Interchange Format has quickly moved forward over the past two years first in automotive and currently starting in domains such as medical and aerospace. This paper describes typical RE collaboration scenarios and what we recommend in order to mitigate risks and thus effectively manage complex supplier relationships. Copyright Copyright 2009 by Vector Consulting Services GmbH and IEEE Computer Society Press. All rights reserved. Any distribution or copying is subject to prior written approval by Vector. Earlier ve...