Wildlife species are being affected in negative ways by transportation infrastructure the world over. Direct mortality, behavior modifications due to sensory impacts, and barrier effects leading to genetic isolation are examples. With expanding human populations and increasing urbanization the challenges to wildlife populations will get worse unless transportation infrastructure modifications and planning take wildlife more into account. In California, especially southern California, recent research has shown how dramatic those impacts can be even for wide ranging, highly mobile species such as the mountain lion. Mountain lion populations are being genetically fragmented and certain populations are threatened with extirpation due to inbreeding, direct highway mortality, and other factors. In this symposium the presenters will describe a variety of issues that transportation infrastructure creates for wildlife in California, especially in southern California, and some of the planned and completed projects that are helping to reduce those negative impacts. The session goal is not only to describe some of the challenges for wildlife and solutions that have been proposed or accomplished, but also to describe the collaborative processes that are being utilized to find solutions. All of the individuals presenting are heavily involved in the intersection between transportation infrastructure and wildlife in southern California, and the projects and challenges they will describe range from completed to ones in the early design stages. The talks will also cover a wide range of spatial scale, from regional planning to site-specific crossing details. They will describe the wide array of issues that have to be faced, integrated, and overcome to improve highway infrastructure for the benefit of wildlife in this highly urbanized and rapidly expanding region. This region is a poster child for the challenges faced all over the world in this realm, and solutions implemented here can help guide such work elsewhere far into the future.