Research on personality disorders (PD) has made progress in several areas. 1) Classification: Most PDs are exaggerations of normal traits and can be described dimensionally, but highly symptomatic PDs may not be well described in this way. Attempts to redefine PDs as variants of Axis I categories, such as depression and bipolar disorder, have been unconvincing. 2) Epidemiology: Recent community surveys suggest that PDs as currently defined have an overall prevalence of around 10%. 3) Etiology: Studies of relationships between PDs and neuroimaging, neuropsychological testing, neurotransmitters, and candidate genes are not related specifically to disorders, although certain markers are linked to traits. The complex pathways to PDs depend on gene-environment interactions. 4) Outcome: PD categories tend to be unstable over time, largely because of symptom reduction. However the traits underlying disorders do not change, and many continue to have poor psychosocial functioning. 5) Treatment: Clinical trials show that a number of psychotherapeutic methods are effective, with improvement often occurring within a few months. In contrast, the results of pharmacological trials have been unimpressive and inconclusive.