A/B testing is the process of testing two variants against each other to see which performs best. You can A/B test website copy, layouts, calls to action, email subject lines and content, ad copy, and more. A/B testing, a common term, is actually a simplistic version of multivariate testing. In multivariate testing, the number of variables or options within those variables is really only constrained by budget, time, and audience size.

A/B or multivariate testing ensures that you're consistently running experiments to improve your marketing. You may find that one call to action earns 30% more conversions than another. That's valuable information to know - instead of guessing. Many email marketing and automation tools will include this type of testing in their software so you can do it automatically as you build a campaign. Don't make the mistake of running off of your assumptions and nothing more.