yambo is an 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. 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. 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. yambo is a Fortran 95 and C program that runs on any computer architecture with a UNIX operating system. It requires 10–1000 Mbytes of RAM and up to 100 processors. It is distributed under the GNU General Public License v2.0. It is interfaced to BLAS, LAPACK, MPI, BLACS, SCALAPACK, and FFTW. It also supports netCDF. The code is used to calculate excited state properties such as quasiparticles, excitons, and plasmons. It uses the results of standard DFT calculations from publicly available codes. The theoretical tools implemented in yambo are TDDFT and the BS equations for the response function and the Dyson equation in the GW approximation for the QPs. The paper is structured as follows. In Section 2, the theoretical background is introduced, including the plasmon-pole approximation and the Bethe-Salpeter equation. Section 3 discusses some numerical aspects, including the random integration method and the Lanczos-Haydock solver of the BS equation. Section 4 provides an overview of the software. Section 5 describes the individual software components. Section 6 outlines the installation instructions. Section 7 provides an example of a typical yambo calculation.yambo is an 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. 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. 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. yambo is a Fortran 95 and C program that runs on any computer architecture with a UNIX operating system. It requires 10–1000 Mbytes of RAM and up to 100 processors. It is distributed under the GNU General Public License v2.0. It is interfaced to BLAS, LAPACK, MPI, BLACS, SCALAPACK, and FFTW. It also supports netCDF. The code is used to calculate excited state properties such as quasiparticles, excitons, and plasmons. It uses the results of standard DFT calculations from publicly available codes. The theoretical tools implemented in yambo are TDDFT and the BS equations for the response function and the Dyson equation in the GW approximation for the QPs. The paper is structured as follows. In Section 2, the theoretical background is introduced, including the plasmon-pole approximation and the Bethe-Salpeter equation. Section 3 discusses some numerical aspects, including the random integration method and the Lanczos-Haydock solver of the BS equation. Section 4 provides an overview of the software. Section 5 describes the individual software components. Section 6 outlines the installation instructions. Section 7 provides an example of a typical yambo calculation.