Unlike their eutherian counterparts, marsupials develop their immune tissues in a non-sterile environment shortly after birth. Neonatal marsupials are therefore reliant on innate and maternally-derived immunological strategies to survive microbial onslaughts until their adaptive immune system develops. To date, developmental studies of the marsupial immune system have largely focused on histological and immunohistochemical techniques. Gaps in our knowledge and understanding of the marsupial immune system remain. Current knowledge of the marsupial immune system and implications for marsupial conservation will be discussed.