Search themes are short phrases you add to an asset group in a Performance Max campaign to tell Google which kinds of searches are relevant to your business. They are a signal about intent, not a list of keywords, and Google uses them alongside your website, assets and audience signals to decide which searches to show your ads for.
How search themes work
Performance Max does not use keywords. Left alone, it reads your landing pages and assets and works out for itself which searches to target. Search themes give you a way to steer that. If a garden landscaper in Surrey adds themes such as “garden design”, “patio installation” and “artificial grass fitting”, Google is more likely to enter auctions for searches around those topics, including ones it might otherwise have missed.
Each asset group accepts a limited number of themes; Google has raised the cap before, so check the current limit in the asset group editor. At the time of writing (October 2026), Google treats search themes with a similar priority to phrase and broad match keywords in ordinary search campaigns. That means an exact-match keyword in a search campaign that matches the query identically will generally win over Performance Max, while a search theme can compete with your broader keywords for the same query.
Themes only add. To stop Performance Max showing on searches you do not want, use account-level negative keywords, brand exclusions or the campaign negative controls, not search themes.
Why it matters
Performance Max can be a black box. Search themes are one of the few direct inputs that shape where it spends on Google Search. Good themes help a new campaign find relevant searches faster, especially if your website is thin or covers several services that Google might not separate on its own.
For a UK business with several distinct services, themes are also a way to keep each asset group focused. A dental practice with one asset group for implants and another for Invisalign can give each its own themes, so the ads and landing pages Google pairs with a search stay matched to the treatment being searched for.
They also matter because of the overlap with your search campaigns. A theme that repeats your main keywords can pull those searches into Performance Max, where you have less reporting and control. Knowing how priority works lets you decide deliberately which campaign should own which searches.
Common mistakes
- Pasting an entire keyword list into search themes as if they were keywords.
- Adding themes that duplicate exact keywords already covered well by a search campaign, causing the two campaigns to compete.
- Using themes in one asset group that belong to a different product or service, which muddles the ads and landing pages Google pairs with them.
- Expecting themes to exclude anything.
- Never checking the search terms insights to see whether the themes changed what Performance Max served.
How to act on it
Write themes that describe the need behind the search, in the words customers use, for each asset group separately. Cover the angles your site might not make obvious: specific services, problems people search for and the product types you most want to sell. Keep your core, high-value searches in exact or phrase match search campaigns, and use themes to extend reach around them.
After a few weeks, open the search terms insights for the campaign and check whether the categories it served match your themes. Pair this with an audience signal for each asset group. Setting up asset groups, themes and exclusions together is part of my Performance Max management.