Alleys represent unrealized community assets that could be transformed by urban planners and managers into ‘green infrastructure’ to simultaneously offer multiple ecological, economic, and social benefits– including urban walkability and mobility, play space and green cover, biodiversity conservation and urban runoff infiltration– and thereby to contribute to a more sustainable urbanism. The paper explores the distribution, physical features, activity patterns, and resident perceptions of alleys in Los Angeles, CA through an integrated mixed-methods strategy. Results show that most alleys in Los Angeles are underutilized and clean, although they can be, and are often perceived as, dirty and unsafe.