Orbital Angular Momentum (OAM) is regarded as one of the potential key technologies for B5G and 6G mobile communications. No matter in the optical transmission or the radio wave transmission, OAM has been concerned as a new dimension (or a degree of freedom) which can provide additional multiplexing and higher spectrum efficiency, e.g. Tbps data rate is aimed with OAM channels multiplexed in the free space backhaul transmission and Pbps data rate is aimed in the optical fiber with OAM mode division multiplexing. In addition, the theoretical study of OAM has already been engaged in the quantum mechanics for a long time. Many researches in the vortex electron show the promising technology in OAM photon radiation and reception, e.g., relativistic electron cyclotron radiation and electron cyclotron masers. Therefore, the 3rd workshop on OAM transmission in ICC 2021 will focus on both the detailed physical theories of OAM and applications in wireless communications. The workshop is expected to be held with the discussion of the state-of-the-art research on OAM transmission and the promising future application