Odd diffusion systems, such as colloidal systems subjected to Lorentz forces and chiral active particles are characterized by a diffusion tensor which has both a symmetric part and an antisymmetric part. The antisymmetric or odd part is a consequence of broken time-reversal symmetry. In the same way that odd viscosity generates normal stresses in the direction perpendicular to shear flow, odd diffusivity generates additional rotational fluxes perpendicular to typical diffusive fluxes. In this presentation, I will be talking about oddity and the diffusion systems performing odd behavior.