Visibility in search results can be bought as well as earned. Search engine marketing, or SEM, is the practice of increasing a website’s visibility on search-engine results pages through paid advertising. The dominant form is pay-per-click advertising on keywords that potential customers type into search engines.

SEM allows advertisers to appear at the moment of intent. Campaigns can be tightly targeted by keyword, location, device, and time. Success is measured by click-through rate, conversion rate, cost per acquisition, and return on ad spend. Continuous testing of ad copy, landing pages, and bids is required to remain competitive.

SEM complements search-engine optimization, which aims for unpaid (organic) visibility. Many organizations use both. The paid channel provides immediate presence and precise control; the organic channel provides longer-term, lower-cost traffic. Together they form the core of most search-related marketing strategies.