Summary QDYN is a boundary element software package to simulate earthquake cycles (tectonic fault slip) under the quasi-dynamic approximation (quasi-static elasticity with radiation damping). The code implements adaptive time stepping and shared-memory (OpenMP) and MPI parallelization to simulate earthquake cycles including seismic and aseismic slip. QDYN includes various forms of rate-and-state friction and state evolution laws. It handles non-planar fault geometries in 3D and 2D elastic media, as well as spring-block simulations. It has a user-friendly matlab interface and graphical output. Features in v1.1 rate-and-state friction, with velocity cut-offs, aging and slip laws heterogeneous frictional properties slow and fast, aseismic and seismic slip transients non-planar faults (currently limited to variable dip, rectangular elements) 3D, 2D and 1D (spring-block) tectonic and transient loads matlab wrapper and graphic output display utilities parallelized for shared memory systems (OpenMP) MPI parallelization normal stress coupling fully coupled with SPECFEM3D via QSB (QDYN-SPECFEM Bridge) Host website https://ydluo.github.io/qdyn/