A large amount of work in perturbative superstring theory is associated to certain limits of string amplitudes with massless (or very low mass) asymptotic states, in simple string backgrounds where computations are feasible. In this talk I will focus on a much less explored regime, that of amplitudes with `highly excited' asymptotic string states, and will give an overview of a formalism (based on covariant coherent state vertex operators) which is particularly efficient for explicit computations involving highly excited strings. I will discuss generic features of `all' 2-point 1-loop amplitudes, eventually focusing on a simple explicit example to illustrate the effectiveness of this new approach, while also making contact with low energy effective field theory results.
