Fast coronal mass ejections (CMEs) are the prime source of space storms and their associated space weather effects. Over the past decades, a variety of solar and heliospheric space missions, such as SOHO, STEREO, SDO or ACE have provided unprecedented remote sensing and in-situ observations of CMEs. The analysis of multipoint space observations has led to a new understanding of their 3D topology. Understanding the 3D topology and interplanetary evolution of CMEs is of key importance to help establish reliable space weather forecasts and to develop methods with which hazardous effects on our modern day technological infrastructure can be mitigated. In my presentation I will summarize the state-of-the-art understanding of CMEs and its scientific and societal benefits.