The existence of symmetry and its tendency to break in aero/hydrodynamics applications are two of the most important aspects of many engineering fields, such as mechanical, aerospace, chemical and process engineering. For instance, the existence of symmetry breaking at a critical Reynolds number confirmed the existence of a bifurcation in expansion pipe flows. Such a symmetry breaking mechanism may cause the appearance of turbulence, which in return increases the mixing, as well as the required pumping power, for several process engineering design applications. Meanwhile, in aerospace applications, the receptivity of symmetric laminar flow to internal/external perturbations may cause flow transition and dramatic change in a local drag coefficient, and heat removal from the surface. The latter needs to be considered in the design step for choosing proper materials that can also bear the unbalanced thermodynamics loads. The applications of symmetry and its breaking are usually inter-disciplinary, and prior knowledge of them is crucial for many real-life applications. Therefore, the current Special Issue, “Aero/Hydrodynamics and Symmetry”, invites original and review works in the field for participation. The scope of this Special Issue includes, but is not limited to, the state of the art computational, theoretical and experimental works that deal with symmetry and its breaking, that are in line with aero-hydrodynamics applications. Recent advances in numerical, theoretical and experimental methodologies, as well as finding new physics, new methodological developments and their limitations, are within the scope of the current Special Issue. Potential topics which are deemed suitable for publication include, but are not limited to: • Mathematical models, such as: symmetry method, homotropy perturbation method (HPM), homotropy analysis method (HAM), lie group, integral transform, etc. • Equilibrium and out of equilibrium thermodynamics and fluid mechanics • Hydrodynamics for symmetric exclusion • Hydrodynamics with multiple higher-form symmetries • Ideal order and dissipative fluids with q-form symmetry • Partial and fractional order differential equations • Finite difference (FDM), finite volume (FVM), and finite element (FEM), smoothed particle hydrodynamics (SPH), moving particle semi-implicit (MPS), lattice Boltzmann (LBM) methods, etc. • Multiphysics phenomena, such as non-Newtonian flows, multiphase flows, phase change, nanofluidic, magnetohydrodynamics (MHD), electrohydrodynamics (EHD), etc. • Symmetry and its breakdown in transitional and turbulent flows