On-shell scattering amplitudes have a multitude of applications. At a practical level, they are needed to quantify Standard Model backgrounds to searches for supersymmetry at the LHC. In maximally supersymmetric theories, they have helped unveil new symmetries such as dual conformal invariance in N=4 super-Yang-Mills theory, and the remarkably good ultraviolet behavior of N=8 supergravity. In many cases, the most efficient way to compute amplitudes is using "on-shell" methods, which reconstruct (multi)-loop amplitudes from lower-point and lower-leg amplitudes using unitarity and factorization properties. I will present an overview of these techniques and highlight some recent applications ranging from phenomenology to supergravity.

We discuss different aspects of scattering amplitudes in maximally supersymmetric Yang-Mills theory. We review their hidden dynamical symmetries and the ways they can restrict the form of the amplitudes, possibly leading to the full integrability of the theory. We also discuss the duality between amplitudes and light-like Wilson loops, as well as the recently discovered new duality with superconformal correlation functions of local BPS operators in the singular light-cone limit.

The so-called "massive" version of IIA string theory is characterized by a non-vanishing Ramond--Ramond flux F_0 (the flux with no indices). This built-in mass parameter helps in several applications; for example, in producing compactifications without massless scalars (in other words, in "stabilizing the moduli"). We review in this talk recent progress in understanding this theory. A crucial point is the quantization of the mass parameter. This manifests itself in holographic duals as the quantization of a certain Chern-Simons level. This can then be used to argue that massive IIA classical solutions can never get strongly coupled. In particular, the massive theory doesn't generate an "M-theory" eleventh dimension, unlike its massless counterpart; this answers a long-standing question.