Mountain lions (Puma concolor) are widely distributed and have apparently expanded their range and increased in abundance in California since the early 1970s. Conflicts between mountain lions and humans have increased during this period. Trends in verified mountain lion damage to livestock and pets are reported for the 26-year period 1972 to 1997. Confirmed mountain lion attacks on humans are summarized for the period 1890 to 1997. This information was analyzed by county, and related to mountain lion habitat suitability, livestock distribution, and human population trends. Health and physical characteristics of a sample of 417 mountain lions were also analyzed for the period 1990 to 1996. Public policy related to mountain lions is discussed with emphasis on trends in conflicts with humans and management implications.