Toast++ is a software suite for image reconstruction in diffuse optical tomography (DOT). It contains a forward solver module using the finite element method for simulating the propagation of light in highly scattering, inhomogeneous biological tissues, such as the brain. The inverse solver module uses an iterative, model-based approach to reconstruct the unknown distributions of absorption and scattering coefficients in the volume of interest from boundary measurements of light transmission. Toast++ consists of a set of libraries written in C++ for sparse linear algebra, finite element computation, and nonlinear image reconstruction. Several command line applications for forward modelling and inverse solution are included. Users who need additional functionality can write their own applications and link to the core Toast++ libraries.