diff --git a/elasticsearch_dsl/search.py b/elasticsearch_dsl/search.py
index c07fe7e71..a6284ad28 100644
--- a/elasticsearch_dsl/search.py
+++ b/elasticsearch_dsl/search.py
@@ -328,6 +328,9 @@ def __init__(self, **kwargs):
         self._query_proxy = QueryProxy(self, "query")
         self._post_filter_proxy = QueryProxy(self, "post_filter")
 
+        self._fields = []
+        self._runtime_mappings = {}
+
     def filter(self, *args, **kwargs):
         return self.query(Bool(filter=[Q(*args, **kwargs)]))
 
@@ -411,6 +414,9 @@ def _clone(self):
         s._highlight_opts = self._highlight_opts.copy()
         s._suggest = self._suggest.copy()
         s._script_fields = self._script_fields.copy()
+        s._fields = self._fields
+        s._runtime_mappings = self._runtime_mappings.copy()
+
         for x in ("query", "post_filter"):
             getattr(s, x)._proxied = getattr(self, x)._proxied
 
@@ -459,6 +465,8 @@ def update_from_dict(self, d):
                     s.setdefault("text", text)
         if "script_fields" in d:
             self._script_fields = d.pop("script_fields")
+        if "runtime_mappings" in d:
+            self._runtime_mappings = d.pop("runtime_mappings")
         self._extra.update(d)
         return self
 
@@ -490,6 +498,48 @@ def script_fields(self, **kwargs):
         s._script_fields.update(kwargs)
         return s
 
+    def runtime_mappings(self, **kwargs):
+        """
+        Define runtime fields to be calculated at query time. See
+        https://www.elastic.co/guide/en/elasticsearch/reference/current/runtime.html
+        for more details.
+
+        Runtime fields are automatically added to the query response.
+
+        Example::
+
+            s = Search()
+            s = s.runtime_mappings(
+                'client_ip': {
+                    'type': 'ip',
+                    'script': '''
+                        String clientip=grok('%{COMMONAPACHELOG}').extract(doc["message"].value)?.clientip;
+                        if (clientip != null) emit(clientip);
+                    '''
+                }
+            )
+
+        """
+        s = self._clone()
+        s._runtime_mappings.update(kwargs)
+        s.fields(*s._runtime_mappings.keys())
+        return s
+
+    def fields(self, *args):
+        """
+        Runtime fields are not indexed or stored, so they will not appear in the _source block if you run a query, but
+        can easily be added to the response by adding the 'fields' clause to the body of the query.
+
+        Example::
+
+            s = Search()
+            s = s.fields("client_ip")
+
+        """
+        s = self._clone()
+        s._fields.extend(args)
+        return s
+
     def source(self, fields=None, **kwargs):
         """
         Selectively control how the _source field is returned.
@@ -678,6 +728,12 @@ def to_dict(self, count=False, **kwargs):
             if self._script_fields:
                 d["script_fields"] = self._script_fields
 
+            if self._runtime_mappings:
+                d["runtime_mappings"] = self._runtime_mappings
+
+            if self._fields:
+                d["fields"] = self._fields
+
         d.update(recursive_to_dict(kwargs))
         return d
 
diff --git a/tests/test_integration/test_search.py b/tests/test_integration/test_search.py
index e3ce061eb..0679f1375 100644
--- a/tests/test_integration/test_search.py
+++ b/tests/test_integration/test_search.py
@@ -16,6 +16,8 @@
 #  under the License.
 
 
+from datetime import datetime
+
 from elasticsearch import TransportError
 from pytest import raises
 
@@ -167,3 +169,35 @@ def test_raw_subfield_can_be_used_in_aggs(data_client):
     authors = r.aggregations.authors
     assert 1 == len(authors)
     assert {"key": "Honza Král", "doc_count": 52} == authors[0]
+
+
+def test_runtime_field(data_client):
+    current_date = datetime.now()
+
+    s = Search(index="git").filter(Q("exists", field="committed_date"))
+    s = s.runtime_mappings(
+        days_since_commit={
+            "type": "long",
+            "script": {
+                "source": """
+                String currentDateStr = params.get('current_date');
+
+                DateTimeFormatter dtf = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
+                LocalDateTime committedDate = doc['committed_date'].value.toLocalDateTime();
+                LocalDateTime currentDate = LocalDateTime.parse(currentDateStr, dtf);
+
+                emit(Duration.between(committedDate, currentDate).toDays());
+            """,
+                "params": {
+                    "current_date": current_date.replace(microsecond=0).isoformat()
+                },
+            },
+        }
+    )
+    response = s.execute()
+
+    for commit in response.hits:
+        assert "days_since_commit" in commit
+
+        committed_date = datetime.fromisoformat(commit.committed_date)
+        assert commit.days_since_commit[0] == (current_date - committed_date).days
diff --git a/tests/test_search.py b/tests/test_search.py
index 4da824182..7144e93a6 100644
--- a/tests/test_search.py
+++ b/tests/test_search.py
@@ -307,6 +307,12 @@ def test_complex_example():
         .filter(Q("term", category="meetup") | Q("term", category="conference"))
         .post_filter("terms", tags=["prague", "czech"])
         .script_fields(more_attendees="doc['attendees'].value + 42")
+        .runtime_mappings(
+            http={
+                "type": "composite",
+                "script": 'emit(grok("%{COMMONAPACHELOG}").extract(doc["message"].value))',
+            }
+        )
     )
 
     s.aggs.bucket("per_country", "terms", field="country").metric(
@@ -342,11 +348,18 @@ def test_complex_example():
                 "aggs": {"avg_attendees": {"avg": {"field": "attendees"}}},
             }
         },
+        "fields": ["http"],
         "highlight": {
             "order": "score",
             "fields": {"title": {"fragment_size": 50}, "body": {"fragment_size": 50}},
         },
         "script_fields": {"more_attendees": {"script": "doc['attendees'].value + 42"}},
+        "runtime_mappings": {
+            "http": {
+                "type": "composite",
+                "script": 'emit(grok("%{COMMONAPACHELOG}").extract(doc["message"].value))',
+            }
+        },
     } == s.to_dict()