--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -34894,16 +34894,28 @@
       },
       "testharness": {
         "dom/collections/HTMLCollection-as-proto-length-get-throws.html": [
           {
             "path": "dom/collections/HTMLCollection-as-proto-length-get-throws.html",
             "url": "/dom/collections/HTMLCollection-as-proto-length-get-throws.html"
           }
         ],
+        "dom/nodes/Element-insertAdjacentElement.html": [
+          {
+            "path": "dom/nodes/Element-insertAdjacentElement.html",
+            "url": "/dom/nodes/Element-insertAdjacentElement.html"
+          }
+        ],
+        "dom/nodes/Element-insertAdjacentText.html": [
+          {
+            "path": "dom/nodes/Element-insertAdjacentText.html",
+            "url": "/dom/nodes/Element-insertAdjacentText.html"
+          }
+        ],
         "dom/nodes/remove-unscopable.html": [
           {
             "path": "dom/nodes/remove-unscopable.html",
             "url": "/dom/nodes/remove-unscopable.html"
           }
         ],
         "js/builtins/Promise-incumbent-global.sub.html": [
           {

--- a/testing/web-platform/meta/dom/interfaces.html.ini
+++ b/testing/web-platform/meta/dom/interfaces.html.ini
@@ -286,35 +286,35 @@
     expected: FAIL
 
   [DOMTokenList interface: document.body.classList must inherit property "supports" with the proper type (7)]
     expected: FAIL
 
   [DOMTokenList interface: calling supports(DOMString) on document.body.classList with too few arguments must throw TypeError]
     expected: FAIL
 
-  [Element interface: element must inherit property "prepend" with the proper type (32)]
+  [Element interface: element must inherit property "prepend" with the proper type (34)]
     expected: FAIL
 
-  [Element interface: element must inherit property "append" with the proper type (33)]
+  [Element interface: element must inherit property "append" with the proper type (35)]
     expected: FAIL
 
-  [Element interface: element must inherit property "query" with the proper type (34)]
+  [Element interface: element must inherit property "query" with the proper type (36)]
     expected: FAIL
 
-  [Element interface: element must inherit property "queryAll" with the proper type (35)]
+  [Element interface: element must inherit property "queryAll" with the proper type (37)]
     expected: FAIL
 
-  [Element interface: element must inherit property "before" with the proper type (40)]
+  [Element interface: element must inherit property "before" with the proper type (42)]
     expected: FAIL
 
-  [Element interface: element must inherit property "after" with the proper type (41)]
+  [Element interface: element must inherit property "after" with the proper type (43)]
     expected: FAIL
 
-  [Element interface: element must inherit property "replaceWith" with the proper type (42)]
+  [Element interface: element must inherit property "replaceWith" with the proper type (44)]
     expected: FAIL
 
   [Document interface: new Document() must inherit property "origin" with the proper type (3)]
     expected: FAIL
 
   [Document interface: new Document() must inherit property "prepend" with the proper type (33)]
     expected: FAIL
 

--- a/testing/web-platform/tests/dom/interfaces.html
+++ b/testing/web-platform/tests/dom/interfaces.html
@@ -305,16 +305,19 @@ interface Element : Node {
   Attr removeAttributeNode(Attr attr);
 
   Element? closest(DOMString selectors);
   boolean matches(DOMString selectors);
 
   HTMLCollection getElementsByTagName(DOMString localName);
   HTMLCollection getElementsByTagNameNS(DOMString? namespace, DOMString localName);
   HTMLCollection getElementsByClassName(DOMString classNames);
+
+  Element? insertAdjacentElement(DOMString where, Element element); // historical
+  void insertAdjacentText(DOMString where, DOMString data); // historical
 };
 
 interface NamedNodeMap {
   readonly attribute unsigned long length;
   getter Attr? item(unsigned long index);
   getter Attr? getNamedItem(DOMString name);
   Attr? getNamedItemNS(DOMString? namespace, DOMString localName);
   Attr? setNamedItem(Attr attr);

new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/dom/nodes/Element-insertAdjacentElement.html
@@ -0,0 +1,91 @@
+<!doctype html>
+<meta charset=utf-8>
+<title></title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+
+<div id="target"></div>
+<div id="parent"><span id=target2></span></div>
+<div id="log" style="visibility:visible"></div>
+<span id="test1"></span>
+<span id="test2"></span>
+<span id="test3"></span>
+<span id="test4"></span>
+<script>
+var target = document.getElementById("target");
+var target2 = document.getElementById("target2");
+
+test(function() {
+  assert_throws("SyntaxError", function() {
+    target.insertAdjacentElement("test", document.getElementById("test1"))
+  });
+
+  assert_throws("SyntaxError", function() {
+    target2.insertAdjacentElement("test", document.getElementById("test1"))
+  });
+}, "Inserting to an invalid location should cause a Syntax Error exception")
+
+test(function() {
+  var el = target.insertAdjacentElement("beforebegin", document.getElementById("test1"));
+  assert_equals(target.previousSibling.id, "test1");
+  assert_equals(el.id, "test1");
+
+  el = target2.insertAdjacentElement("beforebegin", document.getElementById("test1"));
+  assert_equals(target2.previousSibling.id, "test1");
+  assert_equals(el.id, "test1");
+}, "Inserted element should be target element's previous sibling for 'beforebegin' case")
+
+test(function() {
+  var el = target.insertAdjacentElement("afterbegin", document.getElementById("test2"));
+  assert_equals(target.firstChild.id, "test2");
+  assert_equals(el.id, "test2");
+
+  el = target2.insertAdjacentElement("afterbegin", document.getElementById("test2"));
+  assert_equals(target2.firstChild.id, "test2");
+  assert_equals(el.id, "test2");
+}, "Inserted element should be target element's first child for 'afterbegin' case")
+
+test(function() {
+  var el = target.insertAdjacentElement("beforeend", document.getElementById("test3"));
+  assert_equals(target.lastChild.id, "test3");
+  assert_equals(el.id, "test3");
+
+  el = target2.insertAdjacentElement("beforeend", document.getElementById("test3"));
+  assert_equals(target2.lastChild.id, "test3");
+  assert_equals(el.id, "test3");
+}, "Inserted element should be target element's last child for 'beforeend' case")
+
+test(function() {
+  var el = target.insertAdjacentElement("afterend", document.getElementById("test4"));
+  assert_equals(target.nextSibling.id, "test4");
+  assert_equals(el.id, "test4");
+
+  el = target2.insertAdjacentElement("afterend", document.getElementById("test4"));
+  assert_equals(target2.nextSibling.id, "test4");
+  assert_equals(el.id, "test4");
+}, "Inserted element should be target element's next sibling for 'afterend' case")
+
+test(function() {
+  var docElement = document.documentElement;
+  docElement.style.visibility="hidden";
+
+  assert_throws("HierarchyRequestError", function() {
+    var el = docElement.insertAdjacentElement("beforebegin", document.getElementById("test1"));
+    assert_equals(el, null);
+  });
+
+  var el = docElement.insertAdjacentElement("afterbegin", document.getElementById("test2"));
+  assert_equals(docElement.firstChild.id, "test2");
+  assert_equals(el.id, "test2");
+
+  el = docElement.insertAdjacentElement("beforeend", document.getElementById("test3"));
+  assert_equals(docElement.lastChild.id, "test3");
+  assert_equals(el.id, "test3");
+
+  assert_throws("HierarchyRequestError", function() {
+    var el = docElement.insertAdjacentElement("afterend", document.getElementById("test4"));
+    assert_equals(el, null);
+  });
+}, "Adding more than one child to document should cause a HierarchyRequestError exception")
+
+</script>

new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/dom/nodes/Element-insertAdjacentText.html
@@ -0,0 +1,76 @@
+<!doctype html>
+<meta charset=utf-8>
+<title></title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<body style="visibility:hidden">
+<div id="target"></div>
+<div id="parent"><span id=target2></span></div>
+<div id="log" style="visibility:visible"></div>
+</body>
+<script>
+var target = document.getElementById("target");
+var target2 = document.getElementById("target2");
+
+test(function() {
+  assert_throws("SyntaxError", function() {
+    target.insertAdjacentText("test", "text")
+  });
+
+  assert_throws("SyntaxError", function() {
+    target2.insertAdjacentText("test", "test")
+  });
+}, "Inserting to an invalid location should cause a Syntax Error exception")
+
+test(function() {
+  target.insertAdjacentText("beforebegin", "test1");
+  assert_equals(target.previousSibling.nodeValue, "test1");
+
+  target2.insertAdjacentText("beforebegin", "test1");
+  assert_equals(target2.previousSibling.nodeValue, "test1");
+}, "Inserted text node should be target element's previous sibling for 'beforebegin' case")
+
+test(function() {
+  target.insertAdjacentText("afterbegin", "test2");
+  assert_equals(target.firstChild.nodeValue, "test2");
+
+  target2.insertAdjacentText("afterbegin", "test2");
+  assert_equals(target2.firstChild.nodeValue, "test2");
+}, "Inserted text node should be target element's first child for 'afterbegin' case")
+
+test(function() {
+  target.insertAdjacentText("beforeend", "test3");
+  assert_equals(target.lastChild.nodeValue, "test3");
+
+  target2.insertAdjacentText("beforeend", "test3");
+  assert_equals(target2.lastChild.nodeValue, "test3");
+}, "Inserted text node should be target element's last child for 'beforeend' case")
+
+test(function() {
+  target.insertAdjacentText("afterend", "test4");
+  assert_equals(target.nextSibling.nodeValue, "test4");
+
+  target2.insertAdjacentText("afterend", "test4");
+  assert_equals(target.nextSibling.nodeValue, "test4");
+}, "Inserted text node should be target element's next sibling for 'afterend' case")
+
+test(function() {
+  var docElement = document.documentElement;
+  docElement.style.visibility="hidden";
+
+  assert_throws("HierarchyRequestError", function() {
+    docElement.insertAdjacentText("beforebegin", "text1")
+  });
+
+  docElement.insertAdjacentText("afterbegin", "test2");
+  assert_equals(docElement.firstChild.nodeValue, "test2");
+
+  docElement.insertAdjacentText("beforeend", "test3");
+  assert_equals(docElement.lastChild.nodeValue, "test3");
+
+  assert_throws("HierarchyRequestError", function() {
+    docElement.insertAdjacentText("afterend", "test4")
+  });
+}, "Adding more than one child to document should cause a HierarchyRequestError exception")
+
+</script>