The structure of the ambient magnetic field and plasma flow in which coronal mass ejections (CMEs) are embedded in, is a decisive factor for the propagation behavior of CMEs as well as their geo-effectiveness. Strong variations of the ambient magnetic field, speed or density, e.g. due to high-speed solar wind streams, interaction with other CMEs or reconnection with the ambient flow, may cause large changes in the kinematics of CMEs, deflection of the propagation direction or deformation of the CME structure. As such, the preconditioning of interplanetary space has immediate consequences for predicting arrival times and impact speeds of CMEs, hence, an important parameter for Space Weather forecasting. Due to the wealth of observational data from multiple viewpoints, over a wide range of wavelengths, and covering various distance ranges, as well as recent progress in simulations, these issues can be adequately addressed. This session focuses on studies covering observations, remote and in-situ, as well as simulations from which the structuring of interplanetary space may be identified and how this may affect disturbances evolving in the inner heliosphere.