Fresh citrus is an important global commodity and a major specialty crop in California. The 2014-15 CA Agricultural Statistics Review places the combined value of oranges, lemons, and tangerines at over $ 2 billion dollars and all three are in the Top 15 Specialty Crops by value. Fresh whole citrus has not experienced an incident of recall, illness, or outbreak and CA citrus production practices and regions appear to significantly limit the environmental risk of preharvest contamination. However, recent serious incidents involving the bacterial pathogen Listeria monocytogenes, associated with CA apple, have prompted proactive measures to more carefully assess postharvest risks and develop validated interventions for citrus system-wide. Confidentially enrolled handlers will participate in a detailed survey for indicator Listeria and L. monocytogenes. The outcome will be the development of model Environmental Monitoring Program (EMP) and guidance in establishing an environmental-zone Master Sanitation Schedule linked to EMP-outcomes for California fresh citrus packinghouses. The anticipated outcomes are expected to include a general overview and report-card of the CA citrus packing environment and identification of potential sources of Listeria related to industry growing regions and harvest/postharvest practices. From this knowledge-gap closing effort, measureable improvements in reduced L. monocytogenes prevalence will result.