What is A/B Testing?

A/B testing is a method of comparing two versions of something (a headline, a landing page, an ad, an email) by showing each to a portion of your audience and measuring which performs better. Because only one element changes at a time, you learn what actually caused the difference rather than guessing. It's the backbone of conversion rate optimization: small, evidence-based improvements compound into large gains. The key is patience and sample size: ending a test too early, before enough people have seen both versions, produces misleading winners.