Health insurers use narrow and tiered networks to lower costs by contracting with, or favoring, selected providers. Little is known about the contemporary effects of narrow or tiered networks on key metrics. The purpose of this systematic review was to synthesize the evidence on how narrow and tiered networks impact cost, access, quality, and patient steering. We searched PubMed, MEDLINE, and Cochrane Central Register of Controlled Trials databases for articles published from January 2000 to June 2020. Both narrow and tiered networks are associated with reduced overall health care costs for most cost-related measures. Evidence pertaining to access to care and quality measures were more limited to a narrow set of outcomes or were weak in internal validity, but generally concluded no systematic adverse effects on narrow or tiered networks. Narrow and tiered networks appear to reduce costs without affecting some quality measures. More research on quality outcomes is warranted.