{\tt yambo} is an {\it ab initio} code for calculating quasiparticle energies
and optical properties of electronic systems within the framework of many-body
perturbation theory and time-dependent density functional theory. Quasiparticle
energies are calculated within the GW approximation for the self-energy.
Optical properties are evaluated either by solving the Bethe--Salpeter equation
or by using the adiabatic local density approximation. {\tt yambo} is a
plane-wave code that, although particularly suited for calculations of periodic
bulk systems, has been applied to a large variety of physical systems. {\tt
yambo} relies on efficient numerical techniques devised to treat systems with
reduced dimensionality, or with a large number of degrees of freedom. The code
has a user-friendly command-line based interface, flexible I/O procedures and
is interfaced to several publicly available density functional ground-state
codes.Comment: This paper describes the features of the Yambo code, whose source is
available under the GPL license at www.yambo-code.or