This paper provides a brief overview on the magnetic field structure and topology within coronal mass ejections (CMEs) in the solar wind. The overview starts summarizing the magnetic field characteristics within CMEs (magnetic clouds) which exhibit large-scale internal magnetic field rotations indicative of helical magnetic flux ropes and those of non flux rope CMEs lacking smooth internal field rotations. The overview continues with a presentation of Ulysses observations showing evidence for mixed magnetic topologies of open and closed field lines within some CMEs followed by a discussion of the magnetic field structure of CMEs near the Sun in relationship with the observed field properties of CMEs in the solar wind. Finally, the to date main open questions concerning the magnetic origin, evolution and fate of CMEs are addressed. ©1999 American Institute of Physics.