This brief examines the efficacy of providing housing mobility assistance to families with vouchers by examining the Housing Opportunity Program in Chicago. To help families move to opportunity neighborhoods, HOP provides housing search counseling and unit referrals, free credit reports and budget counseling, transportation to view units, expedited housing inspections, workshops on landlord-tenant law, and post-move support. The authors find that voucher holders who enroll in HOP and receive mobility services are significantly more likely to move to opportunity neighborhoods. Vulnerable households, large families, black households and public housing relocatees are less likely to move to opportunity neighborhoods. [View the corresponding press release]