As described by Sampson et al. in 1997, collective efficacy describes a neighborhood-level process that is important to understanding variation in crime rates across neighborhoods. Collective efficacy involves both the willingness of individuals in a neighborhood to work together toward a common goal, such as crime control, and mutual trust. Since the discussion of collective efficacy in the initial publication in 1997, collective efficacy has been an important new addition to criminology's understanding of the causes of crime across neighborhoods.