More than half of people with severe mental illness are lonely, the subjective state associated with social isolation and lack of desired relationships. Their loneliness is related to impaired ability to make and keep friends, lack of opportunities to participate in social activities, and stigma associated with mental illness that creates barriers between them and their communities. Treatment for people with severe mental illness often fails to include social network interventions that have the potential to decrease loneliness. Knowledge of social network interventions-their characteristics, effectiveness, and applicability for specific patients-can guide nurses' use of these treatment modalities.