Coronal magnetic activity is what makes Cool Stars special and distinguishes them from hotter stars without magnetic dynamos. Coronal activity also shapes the environment of many extrasolar planets, giving rise to a completely new perspective why we care about magnetic phenomena. While coronal magnetic activity has been studied for a long time, there are new and exciting insights from recent solar and stellar missions, and we would like to provide a forum to bring the stellar and solar astronomers together and discuss synergies from both fields.

This community collects the presentations given at the 18th "Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun" (also known as "Cool Stars")  http://coolstars18.net held in Flagstaff, Arizona, from Monday, June 9 through Friday, June 13, 2014.

Coronal magnetic activity is what makes Cool Stars special and distinguishes them from hotter stars without magnetic dynamos. Coronal activity also shapes the environment of many extrasolar planets, giving rise to a completely new perspective why we care about magnetic phenomena. While coronal magnetic activity has been studied for a long time, there are new and exciting insights from recent solar and stellar missions, and we would like to provide a forum to bring the stellar and solar astronomers together and discuss synergies from both fields.

In two key areas there is significant observational progress in the last few years:

1. New solar observations, especially IRIS (Interface Region Imaging Spectrograph) and SDO/AIA (Solar Dynamics Observatory, Atmospheric Imaging Assembly) have significantly improved the spatial and temporal resolution of solar observations, as well as their spatial/temporal/temperature coverage.
2. The sample size of stellar activity surveys has exploded, specifically due to the data from Kepler and COROT. We are now at a crucial stage to understand and reap the wealth of such observations, especially in the light of future high-energy missions like Athena+, which is now very likely to been selected by ESA for the L2 launch opportunity.

There is an intimate connection between the activity of our Sun and cool stars. Almost all interpretation of coronal activity starts from the Sun, where observations with a spatial and temporal resolution that is unmatched in stellar astrophysics are possible. On the other hand, active stars provide for more energetic events than commonly observed in our Sun, so that the stellar perspective can help to extend models to a wider range, e.g. to explain the so so-called super-flares.