CIAO performs DNS and LES with multiphysics effects (multiphase, combustion, soot, spark, …). It is a structured, arbitrary order, finite difference code with compressible and incompressible/low-Mach solvers. Moving meshes are supported and overset meshes can be used for local mesh refinement. Spatial and temporal staggering is used to increase the accuracy of stencils. The sub-filter model for the momentum equations is an eddy viscosity concept in form of the dynamic Smagorinsky model with Lagrangian averaging along fluid particle trajectories.The compressible solver uses a low-storage five-stage, explicit Runge-Kutta method for time integration. The low-Mach solver uses Crank-Nicolson time advancement along with an iterative predictor corrector scheme. The Poisson equation for the pressure is solved by the multi-grid HYPRE solver. Momentum equations are spatially discretized with central schemes of arbitrary order, while for scalar equations various different schemes (WENO, HOUC, QUICK, BQUICK, …) are available. Temperature and species equations are advanced by utilizing a Strang operator splitting. The chemistry operator uses a time-implicit backward difference method (CVODE).