In the last decade, vast improvements have been obtained in our observational capabilities of the solar atmosphere. New spectral windows have been opened by space-based facilities, avoiding the influence of Earth's atmosphere but at the expense of telescope aperture and instrument flexibility. At ground-based observatories, efficient adaptive optics systems and novel instrumentation have allowed existing telescopes to push the spatial resolution closer to diffraction limit from the visible to the near-infrared. Yet, when compared with realistic numerical 3D simulations of solar magneto-convection, it is clear that we are still not resolving the fundamental scales at work in the solar atmosphere, which might be as small as few tens of km and of the order of seconds. At the same time, the critical role of the magnetic field as a main agent in shaping the solar atmosphere and its dynamics, implies the need for accurate and precise high-cadence polarimetric measurements, as well as interpretational tools to obtain a quantitative knowledge of solar magnetism throughout the atmosphere.

A number of innovative solar telescopes working in the optical and infrared range has been by now proposed by the international solar physics community. In particular, technological developments, including the feasibility of air-cooled, open telescopes, have allowed for the planning of facilities with apertures sensibly larger than the existing evacuated telescopes. Several of these projects have just become operational or are nearly so: the balloon-borne 1-m telescope SUNRISE first flew in June 2009; the recently commissioned 1.6 m off-axis New Solar Telescope is producing first results; the German 1.5 m on-axis telescope GREGOR recently achieved first light; the next generation 4-m US-led Advanced Technology Solar Telescope has been funded for construction and is scheduled for first light in 2017. Furthermore, several other projects are in various stages of their design (e.g. the 1.5 m coronograph COSMO optimized for measurements of the coronal magnetic field; the 2-m Indian National Large Solar Telescope; the Chinese 1-m Space Solar Telescope; the 4-m European Solar Telescope; the Japanese-led project for the 1.5 m optical telescope aboard Solar-C; the Chinese 8-m Giant Solar Telescope).

New challenges will accompany operations of these advanced facilities.
The foreseen use of multiple high speed, large format scientific cameras which will increase enormously the data volume with respect to current standards, likely approaching hundreds of TB daily, is just an example. As the pioneering efforts with the AIA/SDO datastream are currently showing, highly innovative solutions will be required in order to efficiently extract accurate scientific results from such large volumes. Further, the scientific output of large telescopes will have to be optimized in order to justify the considerable resources invested. For ground-based telescopes, this might require developing robust data reduction pipelines to provide science-ready data to a large user base, as well as adopting more efficient modes of operation, e.g. scheduling observations on a flexible basis in order to best match science programs to observing conditions.

Discussion on these issues within the community is just starting. In the next few years however, we expect that the operation and scientific results of new facilities coming online, as well as instrumental upgrades in existing telescopes (including developments of Multi-Conjugate AO, coronal polarimetry, and tests with different types of observing modes) will yield much novel insight into the peculiarities and possibilities of observations with large solar telescopes.

This two-days long Special Session, to be held within the next IAU General Assembly in August 2012 in Beijing, has been planned to discuss these topics. The Special Session will represent a timely and focused opportunity to review, within the community at large, the current status and results of the new telescopes , discuss strategies to optimize their scientific return, and address critical issues for the development of future facilities that will be at the forefront of solar astrophysics in the next decades.