diff --git a/docs/dom.md b/docs/dom.md
index 9bb54c38..c489d165 100644
--- a/docs/dom.md
+++ b/docs/dom.md
@@ -1543,7 +1543,19 @@ use VeeWee\Xml\Dom\Document;
 use function VeeWee\Xml\Dom\Xpath\Configurator\functions;
 
 $doc = Document::fromXmlFile('data.xml');
-$xpath = $doc->xpath(functions(['has_multiple']));
+$xpath = $doc->xpath(functions(['has_multiple' => has_multiple(...)]));
+```
+
+#### namespaced_functions
+
+Registers a list of namespaced functions to the XPath object, allowing you to use `prefix:somefunction()` inside your XPath query.
+
+```php
+use VeeWee\Xml\Dom\Document;
+use function VeeWee\Xml\Dom\Xpath\Configurator\namespaced_functions;
+
+$doc = Document::fromXmlFile('data.xml');
+$xpath = $doc->xpath(namespaced_functions('http://ns', 'prefix', ['has_multiple' => has_multiple(...)]));
 ```
 
 #### namespaces
diff --git a/docs/xslt.md b/docs/xslt.md
index ba3ea024..8cbf7342 100644
--- a/docs/xslt.md
+++ b/docs/xslt.md
@@ -58,7 +58,22 @@ use function VeeWee\Xml\Xslt\Configurator\functions;
 
 $processor = Processor::fromTemplateDocument(
     Document::fromXmlFile('xml-to-yaml-converter.xslt'),
-    functions(['ucfirst'])
+    functions(['ucfirst' => ucfirst(...)])
+);
+```
+
+#### namespaced_functions
+
+Registers specific namespaced functions to the XSLTProcessor object, allowing you to use `prefix:function('ucfirst',string(uid))` inside your XSLT Template.
+
+```php
+use VeeWee\Xml\Dom\Document;
+use VeeWee\Xml\Xslt\Processor;
+use function VeeWee\Xml\Xslt\Configurator\namespaced_functions;
+
+$processor = Processor::fromTemplateDocument(
+    Document::fromXmlFile('xml-to-yaml-converter.xslt'),
+    namespaced_functions('http://ns', ['ucfirst' => ucfirst(...)])
 );
 ```
 
diff --git a/src/Xml/Dom/Xpath/Configurator/functions.php b/src/Xml/Dom/Xpath/Configurator/functions.php
index cbc3ed7f..7b4eb807 100644
--- a/src/Xml/Dom/Xpath/Configurator/functions.php
+++ b/src/Xml/Dom/Xpath/Configurator/functions.php
@@ -8,7 +8,7 @@
 use Dom\XPath;
 
 /**
- * @param non-empty-list<string> $functions
+ * @param array<string, (callable(mixed...): mixed)> $functions
  *
  * @return Closure(XPath): XPath
  */
diff --git a/src/Xml/Dom/Xpath/Configurator/namespaced_functions.php b/src/Xml/Dom/Xpath/Configurator/namespaced_functions.php
new file mode 100644
index 00000000..f8479a97
--- /dev/null
+++ b/src/Xml/Dom/Xpath/Configurator/namespaced_functions.php
@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace VeeWee\Xml\Dom\Xpath\Configurator;
+
+use Closure;
+use Dom\XPath;
+
+/**
+ * @param array<string, (callable(mixed...): mixed)> $functions
+ *
+ * @return Closure(XPath): XPath
+ */
+function namespaced_functions(string $namespace, string $prefix, array $functions): Closure
+{
+    return static function (XPath $xpath) use ($namespace, $prefix, $functions) : XPath {
+        namespaces([$prefix => $namespace])($xpath);
+        foreach ($functions as $functionName => $callback) {
+            $xpath->registerPhpFunctionNS($namespace, $functionName, $callback);
+        }
+
+        return $xpath;
+    };
+}
diff --git a/src/Xml/Xslt/Configurator/functions.php b/src/Xml/Xslt/Configurator/functions.php
index 210b1705..15a383e2 100644
--- a/src/Xml/Xslt/Configurator/functions.php
+++ b/src/Xml/Xslt/Configurator/functions.php
@@ -8,9 +8,7 @@
 use XSLTProcessor;
 
 /**
- * TODO : Add support for callables : https://wiki.php.net/rfc/improve_callbacks_dom_and_xsl (either here or through a separate configurator)
- *
- * @param non-empty-list<string> $functions
+ * @param array<string, (callable(mixed...): mixed)> $functions
  *
  * @return Closure(XSLTProcessor): XSLTProcessor
  */
diff --git a/src/Xml/Xslt/Configurator/namespaced_functions.php b/src/Xml/Xslt/Configurator/namespaced_functions.php
new file mode 100644
index 00000000..f0d31a05
--- /dev/null
+++ b/src/Xml/Xslt/Configurator/namespaced_functions.php
@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace VeeWee\Xml\Xslt\Configurator;
+
+use Closure;
+use XSLTProcessor;
+
+/**
+ * @param array<string, (callable(mixed...): mixed)> $functions
+ *
+ * @return Closure(XSLTProcessor): XSLTProcessor
+ */
+function namespaced_functions(string $namespace, array $functions): Closure
+{
+    return static function (XSLTProcessor $processor) use ($namespace, $functions) : XSLTProcessor {
+        foreach ($functions as $functionName => $callback) {
+            $processor->registerPhpFunctionNS($namespace, $functionName, $callback);
+        }
+
+        return $processor;
+    };
+}
diff --git a/src/bootstrap.php b/src/bootstrap.php
index 392fd8e9..1341e878 100644
--- a/src/bootstrap.php
+++ b/src/bootstrap.php
@@ -86,6 +86,7 @@
         'Xml\Dom\Validator\xsd_validator' => __DIR__.'/Xml/Dom/Validator/xsd_validator.php',
         'Xml\Dom\Xpath\Configurator\all_functions' => __DIR__.'/Xml/Dom/Xpath/Configurator/all_functions.php',
         'Xml\Dom\Xpath\Configurator\functions' => __DIR__.'/Xml/Dom/Xpath/Configurator/functions.php',
+        'Xml\Dom\Xpath\Configurator\namespaced_functions' => __DIR__.'/Xml/Dom/Xpath/Configurator/namespaced_functions.php',
         'Xml\Dom\Xpath\Configurator\namespaces' => __DIR__.'/Xml/Dom/Xpath/Configurator/namespaces.php',
         'Xml\Dom\Xpath\Configurator\php_namespace' => __DIR__.'/Xml/Dom/Xpath/Configurator/php_namespace.php',
         'Xml\Dom\Xpath\Locator\evaluate' => __DIR__.'/Xml/Dom/Xpath/Locator/evaluate.php',
@@ -170,6 +171,7 @@
         'Xml\Xslt\Configurator\all_functions' => __DIR__.'/Xml/Xslt/Configurator/all_functions.php',
         'Xml\Xslt\Configurator\functions' => __DIR__.'/Xml/Xslt/Configurator/functions.php',
         'Xml\Xslt\Configurator\loader' => __DIR__.'/Xml/Xslt/Configurator/loader.php',
+        'Xml\Xslt\Configurator\namespaced_functions' => __DIR__.'/Xml/Xslt/Configurator/namespaced_functions.php',
         'Xml\Xslt\Configurator\parameters' => __DIR__.'/Xml/Xslt/Configurator/parameters.php',
         'Xml\Xslt\Configurator\profiler' => __DIR__.'/Xml/Xslt/Configurator/profiler.php',
         'Xml\Xslt\Configurator\security_preferences' => __DIR__.'/Xml/Xslt/Configurator/security_preferences.php',
diff --git a/tests/Xml/Dom/Xpath/Configurator/FunctionsTest.php b/tests/Xml/Dom/Xpath/Configurator/FunctionsTest.php
index 1a17054a..5d8102ac 100644
--- a/tests/Xml/Dom/Xpath/Configurator/FunctionsTest.php
+++ b/tests/Xml/Dom/Xpath/Configurator/FunctionsTest.php
@@ -16,7 +16,7 @@ public function test_it_can_evaluate_with_php_function(): void
         $doc = Document::fromXmlString(
             $xml = '<hello><item>Jos</item></hello>'
         );
-        $xpath = Xpath::fromDocument($doc, Xpath\Configurator\functions(['str_replace']));
+        $xpath = Xpath::fromDocument($doc, Xpath\Configurator\functions(['str_replace' => str_replace(...)]));
 
         $result = $xpath->evaluate('php:functionString("str_replace", "J", "B", string(//item))', Type\string());
         static::assertSame($result, 'Bos');
diff --git a/tests/Xml/Dom/Xpath/Configurator/NamespacedFunctionsTest.php b/tests/Xml/Dom/Xpath/Configurator/NamespacedFunctionsTest.php
new file mode 100644
index 00000000..7c7f852e
--- /dev/null
+++ b/tests/Xml/Dom/Xpath/Configurator/NamespacedFunctionsTest.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace VeeWee\Tests\Xml\Dom\Xpath\Configurator;
+
+use PHPUnit\Framework\TestCase;
+use Psl\Type;
+use VeeWee\Xml\Dom\Document;
+use VeeWee\Xml\Dom\Xpath;
+
+final class NamespacedFunctionsTest extends TestCase
+{
+    public function test_it_can_evaluate_with_php_function(): void
+    {
+        $doc = Document::fromXmlString(
+            $xml = '<hello><item>Jos</item></hello>'
+        );
+        $xpath = Xpath::fromDocument($doc, Xpath\Configurator\namespaced_functions(
+            'http://my-ns',
+            'my',
+            ['str_replace' => str_replace(...)]
+        ));
+
+        $result = $xpath->evaluate('my:str_replace("J", "B", string(//item))', Type\string());
+        static::assertSame($result, 'Bos');
+    }
+}
diff --git a/tests/Xml/Xslt/Configurator/FunctionsTest.php b/tests/Xml/Xslt/Configurator/FunctionsTest.php
index 105d64b7..cf17e5a9 100644
--- a/tests/Xml/Xslt/Configurator/FunctionsTest.php
+++ b/tests/Xml/Xslt/Configurator/FunctionsTest.php
@@ -16,7 +16,7 @@ public function test_it_can_use_php_functions(): void
     {
         $processor = Processor::fromTemplateDocument(
             $this->createTemplate(),
-            functions(['strtoupper'])
+            functions(['strtoupper' => strtoupper(...)])
         );
 
         $result = $processor->transformDocumentToString(
@@ -36,7 +36,7 @@ public function test_it_throws_exception_on_unkown_function(): void
     {
         $processor = Processor::fromTemplateDocument(
             $this->createTemplate(),
-            functions(['substr'])
+            functions(['substr' => substr(...)])
         );
         $doc = Document::fromXmlString(
             <<<EOXML
diff --git a/tests/Xml/Xslt/Configurator/NamespacedFunctionsTest.php b/tests/Xml/Xslt/Configurator/NamespacedFunctionsTest.php
new file mode 100644
index 00000000..a3b2978f
--- /dev/null
+++ b/tests/Xml/Xslt/Configurator/NamespacedFunctionsTest.php
@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace VeeWee\Tests\Xml\Xslt;
+
+use PHPUnit\Framework\TestCase;
+use VeeWee\Xml\Dom\Document;
+use VeeWee\Xml\Exception\RuntimeException;
+use VeeWee\Xml\Xslt\Processor;
+use function VeeWee\Xml\Xslt\Configurator\namespaced_functions;
+
+final class NamespacedFunctionsTest extends TestCase
+{
+    public function test_it_can_use_php_functions(): void
+    {
+        $processor = Processor::fromTemplateDocument(
+            $this->createTemplate(),
+            namespaced_functions('http://my-xls', ['strtoupper' => strtoupper(...)])
+        );
+
+        $result = $processor->transformDocumentToString(
+            Document::fromXmlString(
+                <<<EOXML
+                    <root>
+                        <hello>World</hello>
+                    </root>
+                EOXML
+            )
+        );
+
+        static::assertSame('WORLD', $result);
+    }
+
+    public function test_it_throws_exception_on_unkown_function(): void
+    {
+        $processor = Processor::fromTemplateDocument(
+            $this->createTemplate(),
+            namespaced_functions('http://my-xls', ['substr' => substr(...)])
+        );
+        $doc = Document::fromXmlString(
+            <<<EOXML
+                <root>
+                    <hello>World</hello>
+                </root>
+            EOXML
+        );
+
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage('strtoupper');
+        $processor->transformDocumentToString($doc);
+    }
+
+    private function createTemplate(): Document
+    {
+        return Document::fromXmlString(
+            <<<EOXML
+                <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+                    xmlns:my="http://my-xls"
+                    xmlns:str="http://exslt.org/strings"
+                    xmlns:xsdl="http://www.w3.org/1999/XSL/Transform">
+                    <xsl:output method="text" omit-xml-declaration="yes" indent="no"/>
+                    <xsl:template match="/root">
+                        <xsl:value-of select="my:strtoupper(string(./hello))"/>
+                    </xsl:template>
+                </xsl:stylesheet>
+            EOXML
+        );
+    }
+}