Understanding the physical mechanisms of solar variability and its effect on Earth and the planets is a central and long-standing problem of astronomy and astrophysics. Variability of a similar nature has been observed in other stars, and investigating their similarities and differences is essential to helping us understand the underlying mechanisms and their impacts on planets. During the past decade multi-wavelength data from several solar and stellar space missions, together with ground-based observations, have provided tremendous amounts of new information about the physical processes on the Sun and solar-type stars. Solar observations have revealed interesting connections between the cyclic variations of the structure, interior dynamics, surface magnetism and coronal phenomena, but it is still unclear where and how magnetic fields are generated in the Sun, and why it has a regular 22-year magnetic cycle. IAU Symposium 264 discusses key observational results, new theoretical ideas and models which address these subjects.
