Facebook Custom Audiences: Turning First-Party Data into Conversions In modern performance marketing, targeting efficiency is no longer optional. As CPMs rise and third-party cookies continue to disappear, advertisers who rely on broad interest targeting alone face declining returns. Facebook Custom Audiences solve this problem by allowing brands to activate first-party data—people who already know, trust, or have interacted with the business. According to Meta benchmarks, remarketing audiences typically convert 2–3x higher than cold traffic, while maintaining a 20–40% lower CPA when properly segmented. This makes Custom Audiences one of the highest-leverage tools inside Meta Ads Manager. This guide explains what Facebook Custom Audiences are, how they fit into the funnel, how to build them correctly, and how to optimize them for scale without wasting budget.