Nova not only allows you to search within specific resources and relationships, you may also globally search across all your resources using the global search input located within the top-navigation bar of the Nova administration panel:
Global Search
You can focus the global search input by pressing / (forward slash) on your keyboard. Pressing ESC (the escape key) will also close the global search input.

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Title / Subtitle Attributes

When a resource is shown within the search results, the results will display the “title” of the resource. For example, a User resource may specify the name attribute as its title. Then, when the resource is shown within the global search results, that attribute will be displayed. To customize the “title” attribute of a resource, you may define a title property on the resource class: 
/**
 * The single value that should be used to represent the resource when being displayed.
 *
 * @var string
 */
public static $title = 'name';
Alternatively, you may override the resource’s title method: 
/**
 * Get the value that should be displayed to represent the resource.
 *
 * @return string
 */
public function title()
{
    return $this->name;
}
You may also display resource’s “avatar” next to the title in the search result by adding an Avatar field to the resource.

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Subtitles

You may also display a smaller “subtitle” attribute within the global search results. The subtitle will be placed directly under the title attribute. In this screenshot, you can see that the Post resource’s author is displayed as a subtitle, allowing quick identification of who wrote a given post:
Global Search
To define a resource’s subtitle, you should override the subtitle method of the resource: 
/**
 * Get the search result subtitle for the resource.
 *
 * @return string
 */
public function subtitle()
{
    return "Author: {$this->user->name}";
}
If your subtitle accesses information on a related resource, you should consider adding the related resource to your resource’s eager load array.

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Customization

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Limiting Global Search Results

You can limit the number of results that are returned via global search for a given resource by overriding the globalSearchResults property on the resource: 
/**
 * The maximum number of results to include when searching globally.
 *
 * @var int
 */
public static $globalSearchResults = 5;

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Global Search Debounce

You can configure the debounce timing of the global search field using the Nova::globalSearchDebounce method. Normally, this method should be called from within your application’s NovaServiceProvider: 
Nova::globalSearchDebounce(1); // 1 second

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Custom Avatars / Covers

If you are building a custom field that you would like to serve as the “avatar image” / cover art for global search results, your field should implement the Laravel\Nova\Contracts\Cover interface. This interface requires you to define a resolveThumbnailUrl method, which should return the URL of your desired “cover art”: 
/**
 * Resolve the thumbnail URL for the field.
 *
 * @return string|null
 */
public function resolveThumbnailUrl()
{
    return 'https://www.example.com/avatar/'.md5(strtolower($this->value)).'?s=300';
}

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Disabling Global Search for a Resource

By default, all Nova resources are globally searchable; however, you may exclude a given resource from the global search by overriding the globallySearchable property on the resource: 
/**
 * Indicates if the resource should be globally searchable.
 *
 * @var bool
 */
public static $globallySearchable = false;

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Disabling Global Search Globally

If you wish to completely disable global search inside of Nova, you can call the withoutGlobalSearch method from your App/Providers/NovaServiceProvider: 
use Laravel\Nova\Nova;

/**
 * Boot any application services.
 *
 * @return void
 */
public function boot()
{
    parent::boot();

    Nova::withoutGlobalSearch();
}