The idea that the strong interactions may be described by a string theory grew out of the Veneziano amplitude and is even older than Quantum Chromodynamics, and the idea that SU(N) gauge theories, at least in 't Hooft's planar limit, may have such a description is only a little younger. The more recent and radical version of this idea is Maldacena-Witten-... gauge-string (AdS/CFT) duality. To learn something about this string theory it is natural to start by focusing upon any degrees of freedom that are manifestly string-like and, in linearly confining theories such as SU($N$) gauge theories, whether in 2+1 or 3+1 dimensions, these are long confining flux tubes.
One can ask what effective string theory describes the dynamics of these flux tubes. Recently there has been substantial analytic progress towards answering this (old) question which, roughly speaking, tells us that the dynamics governing very long flux tubes is, to a certain approximation, that of a Nambu-Goto free bosonic string theory. Simultaneously, numerical lattice calculations of the the low-lying excitations of closed flux tubes in D=2+1 and D=3+1 SU(N) gauge theories have been telling us that their energies are typically remarkably close to those of the free bosonic string theory even for shorter flux tubes, where the flux tube length is on the order of its (expected) intrinsic width and, naively, they look nothing like strings.
The apparent universality of the string description has motivated calculations in simpler theories (certain spin models etc.) where dualities can be exploited to allow very accurate calculations of very long flux tubes. These reveal clearly the logarithmic growth of the flux tube, now also being seen in gauge theories. The effective string description is also being extended to finite temperature where novel features arise and are being observed. The universality also motivates theoretical calculations, in the context of gauge-gravity duality, where using suitable confining backgrounds it has been successfully checked, and more detailed properties, such as those to do with the intrinsic flux tube width, have begun to be calculated. On the lattice side, there have also been recent lattice calculations that are beginning to give useful information on this intrinsic width.
In related field theories flux tubes can be visible already semiclassically, and in certain cases, given enough supersymmetry, analytic calculations are feasible. Again in the last few years there has been substantial progress on understanding such flux tubes, which are in calculable universality classes that are different from QCD.
On the field theory side, the dynamics of confinement is not yet under analytic control and, indeed, one hopes that an effective string action for the large N theory will eventually either encode (or at least illuminate) that dynamics. But in any case, this dynamics is certainly expected to play a role in determining interesting non-universal aspects of the effective string theory as well the apparent precocious onset of its universal aspects. There have been many ideas tested using lattice gauge theory calculations and there has also been significant progress in understanding non-Abelian solitonic objects that may be dynamically generated and may drive confinement in certain gauge theories. Simultaneously significant progress has been made in reproducing the confining vacuum of SU(N) gauge theories in D=2+1 within a Hamiltonian approach.
In our workshop we had many of the leading figures in all these developments and in some related areas. The main purpose was to inform these different communities of the progress being made in all these related areas and hence to focus attention on problems that were interesting and where progress was being made using different conceptual frameworks and techniques. The focus was therefore on a substantial number of review talks, often reviewing the work done in a particular area over the last decade, together with a detailed presentation of the most recent work (some unpublished) where significant progress was being made. To make this really work we had extended discussion sessions in the afternoons, led by discussion leaders who had been asked to prepare a number of topics for discussion that arose from the morning and early afternoon talks. These discussions proved very useful -- often being animated and involving many of the participants. In this way this Workshop has helped to set the agenda for these problems amongst these overlapping communities of theoretical high energy physics.