  Magnetic oxyselenides have been the topic of research for several decades
being first of interest in the context of photoconductivity and
thermoelectricity owing to their intrinsic semiconducting properties and
ability to tune the energy gap through metal ion substitution. More recently,
interest in the oxyselenides has experienced a resurgence owing to the possible
relation to strongly correlated phenomena given the fact that many oxyslenides
share a similar structure to unconventional superconducting pnictides and
chalcogenides. The two dimensional nature of many oxyselenide systems also
draws an analogy to cuprate physics where a strong interplay between
unconventional electronic phases and localised magnetism has been studied for
several decades. It is therefore timely to review the physics of the
oxyselenides in the context of the broader field of strongly correlated
magnetism and electronic phenomena. Here we review the current status and
progress in this area of research with the focus on the influence of
lanthanides and transition metal ions on the intertwined magnetic and
electronic properties of oxyselenides. The emphasis of the review is on the
magnetic properties and comparisons are made with iron based pnictide and
chalcogenide systems.
