Stormwater biofilters (also called rain gardens, bioretention systems, and bioswales) are used to manage stormwater runoff in urbanized environments. Some benefits of biofilters include flood prevention, stormwater runoff water quality improvement, and wildlife habitat. This technology has been implemented on a larger scale in southeast Australia, but cities and counties in southern California just beginning to construct biofilter systems to manage stormwater runoff. Biofilters tend to be larger in southern California than in southeast Australia. Differences in rainfall patterns likely affect biofilter function. Southern California has much longer periods between rain events than southeast Australia, providing challenges to establishing and maintaining vegetation in biofilters. The use of biofilters for restoring predevelopment flow regimes has been studied in a peri-urban watershed in southeast Australia, but flow regime restoration is not likely in highly urbanized locations in both Australia and southern California. However, stormwater runoff treatment and harvesting in decentralized biofilters could substantially reduce storm flows and improve water quality in receiving waters while improving urban water supply and extending the life of existing stormwater management infrastructure.