  We introduce libdlr, a library implementing the recently introduced discrete
Lehmann representation (DLR) of imaginary time Green's functions. The DLR basis
consists of a collection of exponentials chosen by the interpolative
decomposition to ensure stable and efficient recovery of Green's functions from
imaginary time or Matsbuara frequency samples. The library provides subroutines
to build the DLR basis and grids, and to carry out various standard operations.
The simplicity of the DLR makes it straightforward to incorporate into existing
codes as a replacement for less efficient representations of imaginary time
Green's functions, and libdlr is intended to facilitate this process. libdlr is
written in Fortran, provides a C header interface, and contains a Python module
pydlr. We also introduce a stand-alone Julia implementation, Lehmann.jl.
