How keyword themes match
Google describes a single keyword theme as representing multiple similar words and phrases. Its example: the theme "bakery" makes an ad eligible to show for "bakery near me," "local bakery" and "cake shop." Google recommends a maximum of 7 to 10 themes per campaign, because adding too many can push the ad onto less relevant searches. Themes can't contain punctuation, URLs or phone numbers, and are capped at 20 characters (10 for Japanese and Chinese). For different products or services, Google suggests separate Smart campaigns, each with its own themes and budget.
Negative keyword themes
Negative keyword themes stop ads from showing on searches that aren't relevant, like "wine glasses" for an optometrist who sells eyeglasses. They behave differently from positive themes. Google's help center says they don't match close variants, so ads can still show on close variations of a negative theme. Google's API documentation adds that a negative theme only blocks the exact given term and behaves like a negative phrase match keyword. On that description, a negative theme of "burger" would block searches containing "burger," such as "burger near me," but not "burgers," which needs its own entry. You add them from the "Keyword themes & search terms report" card or straight from the search terms report.
Keyword themes vs search themes
Performance Max has a similar-sounding input called search themes, and they are a different feature. A search theme is a signal you add to an asset group to tell Google's AI what your customers search for, and Google's API documentation says the criterion is used only in Performance Max campaigns. A keyword theme is the targeting itself in a Smart campaign. In a Smart campaign, the search terms report is where you check what your themes actually matched and turn off searches that don't fit.
Common questions
Does a negative keyword theme block close variants?
No. Google says negative keyword themes don't match close variants, so ads might still show on close variations. Add plurals and misspellings you want blocked as separate negative themes.
How many keyword themes should a Smart campaign have?
Google recommends aiming for a maximum of 7 to 10. Because each theme already covers many similar searches, adding too many can make your ad show on less relevant searches.
Are keyword themes the same as keywords?
They are similar, but Google says a single keyword theme can represent multiple keywords, so you don't need an exhaustive keyword list. Google expands each theme to similar searches.
Are keyword themes the same as Performance Max search themes?
No. Keyword themes are the targeting in a Smart campaign. Search themes are a signal you add to a Performance Max asset group to tell Google what your customers search for.