These are the Proceedings of Colloquium No. 153 of the International Astro- nomical Union, held at Makuhari near Tokyo on May 22 - 26, 1995, and hosted by the National Astronomical Observatory. This meeting was intended to be an interdisciplinary meeting between re- searchers of solar and stellar activity, in order for them to exchange the newest information in each field. While each of these areas has seen remarkable advances in recent years, and while the researchers in each field have felt that information from the other's domain would be extremely useful in their own work, there have not...