diff --git a/src/Constants.php b/src/Constants.php
index 1a1f2656..7b39c159 100644
--- a/src/Constants.php
+++ b/src/Constants.php
@@ -152,4 +152,7 @@ class Constants extends \SimpleSAML\XML\Constants
     public const XMLENC_ELEMENT = 'http://www.w3.org/2001/04/xmlenc#Element';
     public const XMLENC_ENCRYPTEDKEY = 'http://www.w3.org/2001/04/xmlenc#EncryptedKey';
     public const XMLENC_EXI = 'http://www.w3.org/2009/xmlenc11#EXI';
+
+    // The namespace for the Elliptic Curve Diffie-Hellman Ephemeral Static (ECDH-ES) algorithm
+    public const XMLENC11_ECDH_ES = 'http://www.w3.org/2009/xmlenc11#ECDH-ES';
 }
diff --git a/src/XML/xenc/AbstractAgreementMethodType.php b/src/XML/xenc/AbstractAgreementMethodType.php
new file mode 100644
index 00000000..009887d0
--- /dev/null
+++ b/src/XML/xenc/AbstractAgreementMethodType.php
@@ -0,0 +1,159 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use DOMElement;
+use SimpleSAML\Assert\Assert;
+use SimpleSAML\XML\Exception\InvalidDOMElementException;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+use SimpleSAML\XML\Exception\TooManyElementsException;
+use SimpleSAML\XML\ExtendableElementTrait;
+use SimpleSAML\XML\XsNamespace as NS;
+
+use function array_pop;
+
+/**
+ * A class implementing the xenc:AbstractAgreementMethodType element.
+ *
+ * @package simplesamlphp/xml-security
+ */
+abstract class AbstractAgreementMethodType extends AbstractXencElement
+{
+    use ExtendableElementTrait;
+
+    /** The namespace-attribute for the xs:any element */
+    public const XS_ANY_ELT_NAMESPACE = NS::OTHER;
+
+
+    /**
+     * AgreementMethodType constructor.
+     *
+     * @param string $algorithm
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\KANonce|null $kaNonce
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\OriginatorKeyInfo|null $originatorKeyInfo
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\RecipientKeyInfo|null $recipientKeyInfo
+     * @param list<\SimpleSAML\XML\SerializableElementInterface> $children
+     */
+    final public function __construct(
+        protected string $algorithm,
+        protected ?KANonce $kaNonce = null,
+        protected ?OriginatorKeyInfo $originatorKeyInfo = null,
+        protected ?RecipientKeyInfo $recipientKeyInfo = null,
+        protected array $children = [],
+    ) {
+        Assert::validURI($algorithm, SchemaViolationException::class); // Covers the empty string
+
+        $this->setElements($children);
+    }
+
+
+    /**
+     * Get the URI identifying the algorithm used by this agreement method.
+     *
+     * @return string
+     */
+    public function getAlgorithm(): string
+    {
+        return $this->algorithm;
+    }
+
+
+    /**
+     * Get the KA-Nonce.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\KANonce|null
+     */
+    public function getKANonce(): ?KANonce
+    {
+        return $this->kaNonce;
+    }
+
+
+    /**
+     * Get the Originator KeyInfo.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\OriginatorKeyInfo|null
+     */
+    public function getOriginatorKeyInfo(): ?OriginatorKeyInfo
+    {
+        return $this->originatorKeyInfo;
+    }
+
+
+    /**
+     * Get the Recipient KeyInfo.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\RecipientKeyInfo|null
+     */
+    public function getRecipientKeyInfo(): ?RecipientKeyInfo
+    {
+        return $this->recipientKeyInfo;
+    }
+
+
+    /**
+     * Initialize an AgreementMethod object from an existing XML.
+     *
+     * @param \DOMElement $xml
+     * @return static
+     *
+     * @throws \SimpleSAML\XML\Exception\InvalidDOMElementException
+     *   if the qualified name of the supplied element is wrong
+     * @throws \SimpleSAML\XML\Exception\MissingAttributeException
+     *   if the supplied element is missing one of the mandatory attributes
+     * @throws \SimpleSAML\XML\Exception\TooManyElementsException
+     *   if too many child-elements of a type are specified
+     */
+    public static function fromXML(DOMElement $xml): static
+    {
+        Assert::same($xml->localName, 'AgreementMethod', InvalidDOMElementException::class);
+        Assert::same($xml->namespaceURI, static::NS, InvalidDOMElementException::class);
+
+        $algorithm = self::getAttribute($xml, 'Algorithm');
+
+        $kaNonce = KANonce::getChildrenOfClass($xml);
+        Assert::maxCount($kaNonce, 1, TooManyElementsException::class);
+
+        $originatorKeyInfo = OriginatorKeyInfo::getChildrenOfClass($xml);
+        Assert::maxCount($originatorKeyInfo, 1, TooManyElementsException::class);
+
+        $recipientKeyInfo = RecipientKeyInfo::getChildrenOfClass($xml);
+        Assert::maxCount($recipientKeyInfo, 1, TooManyElementsException::class);
+
+        $children = self::getChildElementsFromXML($xml);
+
+        return new static(
+            $algorithm,
+            array_pop($kaNonce),
+            array_pop($originatorKeyInfo),
+            array_pop($recipientKeyInfo),
+            $children,
+        );
+    }
+
+
+    /**
+     * Convert this AgreementMethod object to XML.
+     *
+     * @param \DOMElement|null $parent The element we should append this AgreementMethod to.
+     * @return \DOMElement
+     */
+    public function toXML(DOMElement $parent = null): DOMElement
+    {
+        $e = $this->instantiateParentElement($parent);
+        $e->setAttribute('Algorithm', $this->getAlgorithm());
+
+        $this->getKANonce()?->toXML($e);
+
+        foreach ($this->getElements() as $child) {
+            $child->toXML($e);
+        }
+
+        $this->getOriginatorKeyInfo()?->toXML($e);
+        $this->getRecipientKeyInfo()?->toXML($e);
+
+        return $e;
+    }
+}
diff --git a/src/XML/xenc/AgreementMethod.php b/src/XML/xenc/AgreementMethod.php
new file mode 100644
index 00000000..3a7bc106
--- /dev/null
+++ b/src/XML/xenc/AgreementMethod.php
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+/**
+ * A class implementing the xenc:AgreementMethod element.
+ *
+ * @package simplesamlphp/xml-security
+ */
+final class AgreementMethod extends AbstractAgreementMethodType
+{
+}
diff --git a/tests/XML/xenc/AgreementMethodTest.php b/tests/XML/xenc/AgreementMethodTest.php
new file mode 100644
index 00000000..64bad77c
--- /dev/null
+++ b/tests/XML/xenc/AgreementMethodTest.php
@@ -0,0 +1,207 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\XML\Chunk;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Constants as C;
+use SimpleSAML\XMLSecurity\TestUtils\PEMCertificatesMock;
+use SimpleSAML\XMLSecurity\Utils\XPath;
+use SimpleSAML\XMLSecurity\XML\ds\{KeyName, X509Certificate, X509Data, X509SubjectName};
+use SimpleSAML\XMLSecurity\XML\xenc\{AbstractAgreementMethodType, AbstractXencElement};
+use SimpleSAML\XMLSecurity\XML\xenc\{AgreementMethod, KANonce, OriginatorKeyInfo, RecipientKeyInfo};
+
+use function dirname;
+use function openssl_x509_parse;
+use function str_replace;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\AgreementMethodTest
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(AbstractAgreementMethodType::class)]
+#[CoversClass(AgreementMethod::class)]
+final class AgreementMethodTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /** @var string */
+    private static string $certificate;
+
+    /** @var string[] */
+    private static array $certData;
+
+
+    /**
+     */
+    public function setUp(): void
+    {
+        self::$testedClass = AgreementMethod::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_AgreementMethod.xml',
+        );
+
+        self::$certificate = str_replace(
+            [
+                '-----BEGIN CERTIFICATE-----',
+                '-----END CERTIFICATE-----',
+                '-----BEGIN RSA PUBLIC KEY-----',
+                '-----END RSA PUBLIC KEY-----',
+                "\r\n",
+                "\n",
+            ],
+            [
+                '',
+                '',
+                '',
+                '',
+                "\n",
+                '',
+            ],
+            PEMCertificatesMock::getPlainCertificate(PEMCertificatesMock::SELFSIGNED_CERTIFICATE),
+        );
+
+        self::$certData = openssl_x509_parse(
+            PEMCertificatesMock::getPlainCertificate(PEMCertificatesMock::SELFSIGNED_CERTIFICATE),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $kaNonce = new KANonce('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $someChunk = new Chunk(DOMDocumentFactory::fromString(
+            '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">some</ssp:Chunk>',
+        )->documentElement);
+
+        $originatorKeyInfo = new OriginatorKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">originator</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed123',
+        );
+
+        $recipientKeyInfo = new RecipientKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">recipient</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed654',
+        );
+
+        $agreementMethod = new AgreementMethod(
+            C::XMLENC11_ECDH_ES,
+            $kaNonce,
+            $originatorKeyInfo,
+            $recipientKeyInfo,
+            [$someChunk],
+        );
+
+        $this->assertEquals(
+            self::$xmlRepresentation->saveXML(self::$xmlRepresentation->documentElement),
+            strval($agreementMethod),
+        );
+    }
+
+
+    public function testMarshallingElementOrdering(): void
+    {
+        $kaNonce = new KANonce('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $someChunk = new Chunk(DOMDocumentFactory::fromString(
+            '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">some</ssp:Chunk>',
+        )->documentElement);
+
+        $originatorKeyInfo = new OriginatorKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">originator</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed321',
+        );
+
+        $recipientKeyInfo = new RecipientKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">recipient</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed654',
+        );
+
+        $agreementMethod = new AgreementMethod(
+            C::XMLENC11_ECDH_ES,
+            $kaNonce,
+            $originatorKeyInfo,
+            $recipientKeyInfo,
+            [$someChunk],
+        );
+
+        // Marshall it to a \DOMElement
+        $agreementMethodElement = $agreementMethod->toXML();
+
+        $xpCache = XPath::getXPath($agreementMethodElement);
+
+        // Test for an KA-Nonce
+        /** @var \DOMElement[] $kaNonceElements */
+        $kaNonceElements = XPath::xpQuery($agreementMethodElement, './xenc:KA-Nonce', $xpCache);
+        $this->assertCount(1, $kaNonceElements);
+
+        // Test ordering of AgreementMethod contents
+        /** @var \DOMElement[] $agreementMethodElements */
+        $agreementMethodElements = XPath::xpQuery(
+            $agreementMethodElement,
+            './xenc:KA-Nonce/following-sibling::*',
+            $xpCache,
+        );
+
+        $this->assertCount(3, $agreementMethodElements);
+        $this->assertEquals('ssp:Chunk', $agreementMethodElements[0]->tagName);
+        $this->assertEquals('xenc:OriginatorKeyInfo', $agreementMethodElements[1]->tagName);
+        $this->assertEquals('xenc:RecipientKeyInfo', $agreementMethodElements[2]->tagName);
+    }
+}
diff --git a/tests/resources/xml/xenc_AgreementMethod.xml b/tests/resources/xml/xenc_AgreementMethod.xml
new file mode 100644
index 00000000..8d3ac53e
--- /dev/null
+++ b/tests/resources/xml/xenc_AgreementMethod.xml
@@ -0,0 +1,20 @@
+<xenc:AgreementMethod xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" Algorithm="http://www.w3.org/2009/xmlenc11#ECDH-ES">
+  <xenc:KA-Nonce>/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:KA-Nonce>
+  <ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">some</ssp:Chunk>
+  <xenc:OriginatorKeyInfo Id="fed123">
+    <ds:KeyName xmlns:ds="http://www.w3.org/2000/09/xmldsig#">testkey</ds:KeyName>
+    <ds:X509Data xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
+      <ds:X509Certificate>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</ds:X509Certificate>
+      <ds:X509SubjectName>/CN=selfsigned.simplesamlphp.org/O=SimpleSAMLphp HQ/L=Honolulu/ST=Hawaii/C=US</ds:X509SubjectName>
+    </ds:X509Data>
+    <ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">originator</ssp:Chunk>
+  </xenc:OriginatorKeyInfo>
+  <xenc:RecipientKeyInfo Id="fed654">
+    <ds:KeyName xmlns:ds="http://www.w3.org/2000/09/xmldsig#">testkey</ds:KeyName>
+    <ds:X509Data xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
+      <ds:X509Certificate>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</ds:X509Certificate>
+      <ds:X509SubjectName>/CN=selfsigned.simplesamlphp.org/O=SimpleSAMLphp HQ/L=Honolulu/ST=Hawaii/C=US</ds:X509SubjectName>
+    </ds:X509Data>
+    <ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">recipient</ssp:Chunk>
+  </xenc:RecipientKeyInfo>
+</xenc:AgreementMethod>