This document discusses A/B testing of emails and landing pages. It explains that A/B testing involves showing different versions of a site to visitors to see which performs better according to goals like purchases or leads. Effective A/B tests identify goals, choose a page or email to test, select an element to vary like headlines or buttons, state a hypothesis, and track results to determine a winner. Examples of testing ideas included formatting, subject lines, "from" lines, button placement, headers and banners. The document emphasizes using data from A/B tests to improve performance rather than personal preferences.