New and emerging diseases are a substantial threat to aquatic animal production and aquatic environments, especially as they can affect both wild and farmed populations. It can be challenging to prioritise the need to learn about a disease and the need to contain or eradicate it, but general principles and approaches apply. This project is focussed on developing a guideline to investigate and understand disease outbreaks of unknown cause. As aquaculture continues to expand at around 6% per annum, disease control strategies will benefit from this approach.