In this age of accountability, the expectation is that therapists will not only provide effective treatment but be able to demonstrate that the treatment is effective. This expectation has given rise to two different perspectives on how to achieve such evidence. One perspective emphasizes “evidencebased practice,” which is based on the premise that specific treatment interventions must have been empirically demonstrated to be effective with specific psychological problems. The other perspective emphasizes “practice-based evidence,” which is based on the premise that effectiveness is more a function of therapist-client collaboration than of specific treatment interventions. This second perspective places a premium on assessing specific treatment processes and outcomes measures, and requires therapists to monitor treatment processes and outcomes. This chapter focuses on the second perspective.