Kakadu National Park is Australia’s premier protected area and one of the few World Heritage areas listed for both its natural and cultural heritage values. Kakadu National Park encompasses vast areas of seasonally inundated wetlands that support an outstanding abundance of biodiversity, particularly birds and fish. The wetlands provide critical resources for the Indigenous landowners and are also amajor tourist attraction. The international importance of Kakadu National Parks’ wetlands is also reflected by their listing under the Ramsar Wetlands Convention. Unfortunately, these wetlands are under substantial threat from a range of high impact invasive alien plants. The response of managers to different invasive alien plants has varied substantially. For example, the response by Kakadu National Park managers to the threat from the alien shrub Mimosa pigra has widely been used as a case study of best practice. The response was rapid, appropriately resourced, consistent over time and well-monitored. In contrast, the response to two aquatic invasive alien grass species, Hymenachne amplexicaulis and Urochloa mutica, has been relatively poor. Subsequently, whereas M. pigra remains under control, with a limited number of small infestations, the alien grasses have spread extensively in recent years and now pose a substantial threat. This chapter explores the history, invasion and management response to invasive alien grass management in Kakadu National Park. We suggest actions that should commence immediately to avoid wasting the past efforts made to save Kakadu National Park’s wetland ecosystems from M. pigra, and prevent their conversion into invasive alien grass dominated systems.