diff --git a/telethon/sessions/memory.py b/telethon/sessions/memory.py
new file mode 100644
index 00000000..330a82c1
--- /dev/null
+++ b/telethon/sessions/memory.py
@@ -0,0 +1,223 @@
+from enum import Enum
+
+from .abstract import Session
+from .. import utils
+from ..tl import TLObject
+from ..tl.types import (
+    PeerUser, PeerChat, PeerChannel,
+    InputPeerUser, InputPeerChat, InputPeerChannel,
+    InputPhoto, InputDocument
+)
+
+
+class _SentFileType(Enum):
+    DOCUMENT = 0
+    PHOTO = 1
+
+    @staticmethod
+    def from_type(cls):
+        if cls == InputDocument:
+            return _SentFileType.DOCUMENT
+        elif cls == InputPhoto:
+            return _SentFileType.PHOTO
+        else:
+            raise ValueError('The cls must be either InputDocument/InputPhoto')
+
+
+class MemorySession(Session):
+    def __init__(self):
+        super().__init__()
+
+        self._dc_id = 0
+        self._server_address = None
+        self._port = None
+        self._auth_key = None
+
+        self._files = {}
+        self._entities = set()
+
+    def set_dc(self, dc_id, server_address, port):
+        self._dc_id = dc_id or 0
+        self._server_address = server_address
+        self._port = port
+
+    @property
+    def server_address(self):
+        return self._server_address
+
+    @property
+    def port(self):
+        return self._port
+
+    @property
+    def auth_key(self):
+        return self._auth_key
+
+    @auth_key.setter
+    def auth_key(self, value):
+        self._auth_key = value
+
+    def close(self):
+        pass
+
+    def save(self):
+        pass
+
+    def delete(self):
+        pass
+
+    def _entity_values_to_row(self, id, hash, username, phone, name):
+        # While this is a simple implementation it might be overrode by,
+        # other classes so they don't need to implement the plural form
+        # of the method. Don't remove.
+        return id, hash, username, phone, name
+
+    def _entity_to_row(self, e):
+        if not isinstance(e, TLObject):
+            return
+        try:
+            p = utils.get_input_peer(e, allow_self=False)
+            marked_id = utils.get_peer_id(p)
+        except TypeError:
+            return
+
+        if isinstance(p, (InputPeerUser, InputPeerChannel)):
+            if not p.access_hash:
+                # Some users and channels seem to be returned without
+                # an 'access_hash', meaning Telegram doesn't want you
+                # to access them. This is the reason behind ensuring
+                # that the 'access_hash' is non-zero. See issue #354.
+                # Note that this checks for zero or None, see #392.
+                return
+            else:
+                p_hash = p.access_hash
+        elif isinstance(p, InputPeerChat):
+            p_hash = 0
+        else:
+            return
+
+        username = getattr(e, 'username', None) or None
+        if username is not None:
+            username = username.lower()
+        phone = getattr(e, 'phone', None)
+        name = utils.get_display_name(e) or None
+        return self._entity_values_to_row(
+            marked_id, p_hash, username, phone, name
+        )
+
+    def _entities_to_rows(self, tlo):
+        if not isinstance(tlo, TLObject) and utils.is_list_like(tlo):
+            # This may be a list of users already for instance
+            entities = tlo
+        else:
+            entities = []
+            if hasattr(tlo, 'chats') and utils.is_list_like(tlo.chats):
+                entities.extend(tlo.chats)
+            if hasattr(tlo, 'users') and utils.is_list_like(tlo.users):
+                entities.extend(tlo.users)
+
+        rows = []  # Rows to add (id, hash, username, phone, name)
+        for e in entities:
+            row = self._entity_to_row(e)
+            if row:
+                rows.append(row)
+        return rows
+
+    def process_entities(self, tlo):
+        self._entities |= set(self._entities_to_rows(tlo))
+
+    def get_entity_rows_by_phone(self, phone):
+        try:
+            return next((id, hash) for id, hash, _, found_phone, _
+                        in self._entities if found_phone == phone)
+        except StopIteration:
+            pass
+
+    def get_entity_rows_by_username(self, username):
+        try:
+            return next((id, hash) for id, hash, found_username, _, _
+                        in self._entities if found_username == username)
+        except StopIteration:
+            pass
+
+    def get_entity_rows_by_name(self, name):
+        try:
+            return next((id, hash) for id, hash, _, _, found_name
+                        in self._entities if found_name == name)
+        except StopIteration:
+            pass
+
+    def get_entity_rows_by_id(self, id, exact=True):
+        try:
+            if exact:
+                return next((id, hash) for found_id, hash, _, _, _
+                            in self._entities if found_id == id)
+            else:
+                ids = (
+                    utils.get_peer_id(PeerUser(id)),
+                    utils.get_peer_id(PeerChat(id)),
+                    utils.get_peer_id(PeerChannel(id))
+                )
+                return next((id, hash) for found_id, hash, _, _, _
+                            in self._entities if found_id in ids)
+        except StopIteration:
+            pass
+
+    def get_input_entity(self, key):
+        try:
+            if key.SUBCLASS_OF_ID in (0xc91c90b6, 0xe669bf46, 0x40f202fd):
+                # hex(crc32(b'InputPeer', b'InputUser' and b'InputChannel'))
+                # We already have an Input version, so nothing else required
+                return key
+            # Try to early return if this key can be casted as input peer
+            return utils.get_input_peer(key)
+        except (AttributeError, TypeError):
+            # Not a TLObject or can't be cast into InputPeer
+            if isinstance(key, TLObject):
+                key = utils.get_peer_id(key)
+                exact = True
+            else:
+                exact = not isinstance(key, int) or key < 0
+
+        result = None
+        if isinstance(key, str):
+            phone = utils.parse_phone(key)
+            if phone:
+                result = self.get_entity_rows_by_phone(phone)
+            else:
+                username, _ = utils.parse_username(key)
+                if username:
+                    result = self.get_entity_rows_by_username(username)
+
+        elif isinstance(key, int):
+            result = self.get_entity_rows_by_id(key, exact)
+
+        if not result and isinstance(key, str):
+            result = self.get_entity_rows_by_name(key)
+
+        if result:
+            entity_id, entity_hash = result  # unpack resulting tuple
+            entity_id, kind = utils.resolve_id(entity_id)
+            # removes the mark and returns type of entity
+            if kind == PeerUser:
+                return InputPeerUser(entity_id, entity_hash)
+            elif kind == PeerChat:
+                return InputPeerChat(entity_id)
+            elif kind == PeerChannel:
+                return InputPeerChannel(entity_id, entity_hash)
+        else:
+            raise ValueError('Could not find input entity with key ', key)
+
+    def cache_file(self, md5_digest, file_size, instance):
+        if not isinstance(instance, (InputDocument, InputPhoto)):
+            raise TypeError('Cannot cache %s instance' % type(instance))
+        key = (md5_digest, file_size, _SentFileType.from_type(instance))
+        value = (instance.id, instance.access_hash)
+        self._files[key] = value
+
+    def get_file(self, md5_digest, file_size, cls):
+        key = (md5_digest, file_size, _SentFileType.from_type(cls))
+        try:
+            return cls(self._files[key])
+        except KeyError:
+            return None