diff --git a/cheuph/attributed_lines.py b/cheuph/attributed_lines.py
index 6055c85..7f089ca 100644
--- a/cheuph/attributed_lines.py
+++ b/cheuph/attributed_lines.py
@@ -1,3 +1,6 @@
+# TODO retrieve attributes of any (x, y) coordinates
+# TODO retrieve attributes of closest existing line (by y coordinate)
+
 import collections
 from typing import Deque, Iterator, List, Optional, Tuple
 
@@ -8,6 +11,7 @@ __all__ = ["Line", "AttributedLines"]
 
 Line = Tuple[Attributes, AttributedText]
 
+
 class AttributedLines:
     """
     AttributedLines is a list of lines of AttributedText that maintains a
@@ -44,26 +48,30 @@ class AttributedLines:
 
     # Modifying functions
 
-    def append_above(self, line: Line) -> None:
+    def append_above(self,
+            attributes: Attributes,
+            text: AttributedText) -> None:
         """
         Append a line above all already existing lines. The existing lines'
         offsets do not change.
         """
 
-        self._lines.appendleft(line)
+        self._lines.appendleft((attributes, text))
         self.upper_offset -= 1
 
-    def append_below(self, line: Line) -> None:
+    def append_below(self,
+            attributes: Attributes,
+            text: AttributedText) -> None:
         """
         Append a line below all already existing lines. The existing lines'
         offsets do not change.
         """
 
-        self._lines.append(line)
+        self._lines.append((attributes, text))
         # lower offset does not need to be modified since it's calculated based
         # on the upper offset
 
-    def expand_above(self, lines: "AttributedLines") -> None:
+    def extend_above(self, lines: "AttributedLines") -> None:
         """
         Prepend an AttributedLines, ignoring its offsets and using the current
         AttributedLines's offsets instead.
@@ -72,7 +80,7 @@ class AttributedLines:
         self._lines.extendleft(lines._lines)
         self.upper_offset -= len(lines)
 
-    def expand_below(self, lines: "AttributedLines") -> None:
+    def extend_below(self, lines: "AttributedLines") -> None:
         """
         Append an AttributedLines, ignoring its offsets and using the current
         AttributedLines's offsets instead.
@@ -111,10 +119,10 @@ class AttributedLines:
         between = self.between(start_offset, end_offset)
 
         while between.upper_offset > start_offset:
-            between.append_above(({}, AT()))
+            between.append_above({}, AT())
 
         while between.lower_offset < end_offset:
-            between.append_below(({}, AT()))
+            between.append_below({}, AT())
 
         return between
 
diff --git a/cheuph/attributed_lines_widget.py b/cheuph/attributed_lines_widget.py
index 1de6bc4..9b65737 100644
--- a/cheuph/attributed_lines_widget.py
+++ b/cheuph/attributed_lines_widget.py
@@ -1,3 +1,5 @@
+# TODO send event on mouse click
+
 from typing import Any, Optional, Tuple
 
 import urwid
diff --git a/cheuph/message.py b/cheuph/message.py
index e5a1634..8472697 100644
--- a/cheuph/message.py
+++ b/cheuph/message.py
@@ -1,4 +1,8 @@
-from typing import Hashable
+from dataclasses import dataclass
+from typing import Hashable, List
+
+from .attributed_lines import AttributedLines
+from .markup import AttributedText
 
 __all__ = ["Id", "Message", "RenderedMessage"]
 
@@ -19,9 +23,10 @@ class Message:
     truncation status.
     """
 
-    pass
-
+    def render(self, width: int) -> RenderedMessage:
+        pass # TODO
 
+@dataclass
 class RenderedMessage:
     """
     A RenderedMessage is the result of rendering a Message. It contains lines
@@ -40,4 +45,6 @@ class RenderedMessage:
     rather the result of rendering a Message.
     """
 
-    pass
+    message_id: Id
+    meta: AttributedText
+    lines: List[AttributedText]
diff --git a/cheuph/message_supply.py b/cheuph/message_supply.py
index 1e674c7..7e70111 100644
--- a/cheuph/message_supply.py
+++ b/cheuph/message_supply.py
@@ -1,3 +1,7 @@
+from typing import List, Optional
+
+from .message import Id, Message
+
 __all__ = ["MessageSupply"]
 
 
@@ -12,4 +16,24 @@ class MessageSupply:
     similar.
     """
 
-    pass
+    # TODO should throw exception if it can't find the message
+    def get(self, message_id: Id) -> Message:
+        pass # TODO
+
+    def children_ids(self, message_id: Id) -> List[Id]:
+        pass # TODO
+
+    def parent_id(self, message_id: Id) -> Optional[Id]:
+        pass # TODO
+
+    def oldest_ancestor_id(self, message_id: Id) -> Id:
+        pass # TODO
+
+    def previous_id(self, message_id: Id) -> Optional[Id]:
+        pass # TODO
+
+    def next_id(self, message_id: Id) -> Optional[Id]:
+        pass # TODO
+
+    def lowest_root_id(self) -> Optional[Id]:
+        pass # TODO
diff --git a/cheuph/message_tree_widget.py b/cheuph/message_tree_widget.py
index 73dd0fc..22e9840 100644
--- a/cheuph/message_tree_widget.py
+++ b/cheuph/message_tree_widget.py
@@ -1,10 +1,13 @@
 from typing import Optional, Set
 
 import urwid
+
 import yaboli
 
+from .attributed_lines import AttributedLines
 from .attributed_lines_widget import AttributedLinesWidget
-from .message import Id
+from .markup import AT, AttributedText
+from .message import Id, RenderedMessage
 from .message_supply import MessageSupply
 from .rendered_message_cache import RenderedMessageCache
 
@@ -34,35 +37,417 @@ class MessageTreeWidget(urwid.WidgetWrap):
     finishes editing it.
     """
 
-    ROOM_IS_EMPTY = "<no messages>"
+    ROOM_IS_EMPTY_MESSAGE = "<no messages>"
 
     def __init__(self,
+            # TODO config
             room: yaboli.Room,
             supply: MessageSupply,
             ) -> None:
 
+        # yaboli.Room, used only for the current nick
         self.room = room
+        # A supply of Message-s
         self.supply = supply
+        # A cache of RenderedMessage-s
         self.rendered = RenderedMessageCache()
-        self.lines = AttributedLinesWidget()
-        self.placeholder = urwid.Filler(urwid.Text(self.ROOM_IS_EMPTY,
+        # The lines that were last rendered
+        self.lines = AttributedLines()
+        #
+        # Widget tha displays self.lines
+        self.lines_widget = AttributedLinesWidget()
+        # A placeholder if there are no messages to display
+        self.placeholder = urwid.Filler(urwid.Text(self.ROOM_IS_EMPTY_MESSAGE,
             align=urwid.CENTER))
 
+        # The id of the message that the cursor is displayed under.
+        self.cursor_id: Optional[Id] = None
         # If the anchor is None, but the cursor isn't, the cursor is used as
         # the anchor.
-        self.cursor: Optional[Id] = None
-        self.anchor: Optional[Id] = None
-        self.anchor_offset = 0
+        self.anchor_id: Optional[Id] = None
+        # The anchor's line's offset on the screen, measured in percent of the
+        # total height. For more information, see the comment above
+        # _get_absolute_offset() and _get_relative_offset().
+        self.anchor_offset = 0.5
 
-        self.folds: Set[Id] = set()
+        # The last known width (use this to invalidate the cache when needed)
+        self.width = 80
+        # Columns per indentation level
+        self.indent_width = 2
+        # Columns at beginning of line that are reserved for date etc.
+        self.meta_width = 6 # "HH:MM "
+        # Columns at the end to mark overlapping lines
+        self.overlap_width = 1
+
+        # Which sub-threads are folded
+        #self.folds: Set[Id] = set() # TODO
 
         super().__init__(self.placeholder)
 
+    @property
+    def usable_width(self) -> int:
+        """
+        The width that's available for everything, while staying inside the
+        bounds of the overlap indicators.
+        """
+
+        return self.width - self.overlap_width
+
+    @property
+    def content_width(self) -> int:
+        """
+        The width that's left over for messages and their indentation
+        information, after meta_width etc. are removed.
+        """
+
+        return self.usable_width - self.meta_width
+
+    # Offsets
+
+    """
+    On offsets:
+
+    An offset of 0.0 describes the middle of the first line on screen, whereas
+    an offset of 1.0 describes the middle of the last line on screen.
+
+    An example:
+
+    line 0 - 0.0
+    line 1 - 0.25
+    line 2 - 0.5
+    line 3 - 0.75
+    line 4 - 1.0
+
+    Let l be a line's index (starts with 0), o the offset and n the number of
+    lines visible on the screen.
+
+    OFFSET -> LINE NUMBER
+
+    l = round(o * (n - 1))
+
+    LINE NUMBER -> OFFSET
+
+    o = l / (n - 1)
+
+    Be careful if only one line is visible on the screen! Setting o to 0.5 is
+    recommended in that case.
+    """
+
+    @staticmethod
+    def _get_absolute_offset(offset: float, height: int) -> int:
+        return round(offset * (height - 1))
+
+    @staticmethod
+    def _get_relative_offset(line: int, height: int) -> float:
+        if height <= 1:
+            return 0.5
+
+        return line / (height - 1)
+
+    @property
+    def absolute_anchor_offset(self) -> int:
+        return self._get_absolute_offset(self.anchor_offset, self.height)
+
+    @absolute_anchor_offset.setter
+    def absolute_anchor_offset(self, offset: int) -> None:
+        self.anchor_offset = self._get_relative_offset(offset, self.height)
+
+    # Message cache operations and maintenance
+
     def invalidate_message(self, message_id: Id) -> None:
-        pass
+        """
+        Invalidate the RenderedMessage cached under message_id.
+        """
+
+        pass # TODO
 
     def invalidate_all_messages(self) -> None:
-        pass
+        """
+        Invalidate all cached RenderedMessage-s.
+        """
+
+        pass # TODO
+
+    # Rendering a single message
+
+    def _render_message(self, message_id: Id, width: int) -> RenderedMessage:
+        """
+        Somehow obtain a RenderedMessage for the specified message_id.
+
+        If the cache does not contain this message yet, or if it contains an
+        invalid message (wrong width), the message is rendered and then added
+        to the cache. Otherwise, the cached message is returned.
+        """
+
+        cached = self.cache.get(message_id)
+
+        if cached.width != width:
+            self.invalidate_message(message_id)
+            cached = None
+
+        if cached is not None:
+            return cached
+
+        message = self.supply.get(message_id)
+        # TODO give current Room to message so it knows the current nick(s)
+        # TODO give current meta format to message
+        rendered = message.render(width)
+        self.cache.set(message_id, rendered)
+        return rendered
+
+    def _render_message_lines(self,
+            message_id: Id,
+            indent: AttributedText = AT(),
+            ) -> AttributedLines:
+        """
+        Render the message with the specified id into AttributedLines.
+
+        The lines have the format:
+
+        <meta><indent><nick and content>
+
+        Each line has the following line-wide attributes:
+
+        - mid - the id of the message
+        - offset - the offset to the message's topmost line
+        """
+
+        width = self.content_width - len(indent)
+        rendered = self._render_message(message_id, width)
+
+        meta = rendered.meta
+        meta_spaces = AT(" " * len(rendered.meta))
+
+        lines = AttributedLines()
+
+        mid = rendered.message_id
+        offset = 0
+
+        lines.append_below({"mid": mid, "offset": offset},
+                meta + indent + rendered.lines[0])
+
+        for line in rendered.lines[1:]:
+            offset += 1
+            lines.append_below({"mid": mid, "offset": offset},
+                    meta_spaces + indent + line)
+
+        return lines
+
+    def _render_cursor(self, indent: AttributedText = AT()) -> AttributedLines:
+        pass # TODO
+
+    # Rendering the tree
+
+    def _render_tree(self, root_id: Id) -> AttributedLines:
+        """
+        A wrapper around _render_subtree(), for ease of use.
+
+        Doesn't adjust the offset; the AttributedLines returned does NOT take
+        into account the attribute_offset.
+        """
+
+        lines = AttributedLines()
+        self.render_subtree(lines, root_id)
+        return lines
+
+    def _render_subtree(self,
+            lines: AttributedLines,
+            root_id: Id,
+            indent: AttributedText = AT(),
+            ) -> None:
+        """
+        Render a (sub-)tree to the AttributedLines specified.
+
+        This function also sets the vertical offset to be 0 on the anchor's
+        first line, or the cursor's first (and only) line if the cursor is the
+        anchor.
+
+        - lines - the AttributedLines object to render to
+        - root_id - the id of the message to start rendering at
+        - indent - the indent string to prepend
+        """
+
+        if self.anchor_id == root_id:
+            lines.lower_offset = -1
+
+        # Render main message (root)
+        rendered = self._render_message_lines(root_id, indent)
+        lines.extend_below(rendered)
+
+        # Determine new indent
+        extra_indent = AT("┃ " if self.cursor_id == root_id else "│ ")
+        new_indent = indent + extra_indent
+
+        # Render children
+        for child_id in self.supply.children_ids(root_id):
+            self._render_subtree(lines, child_id, new_indent)
+
+        # Render cursor if necessary
+        if self.cursor_id == root_id:
+            # The cursor also acts as anchor if anchor is not specified
+            if self.anchor_id is None:
+                lines.lower_offset = -1
+
+            cursor_indent = indent + AT("┗━")
+            lines.extend_below(self._render_cursor(indent))
+
+    def _render_tree_containing(self, message_id: Id) -> AttributedLines:
+        """
+        Similar to _render_tree(), but finds the root of the specified message
+        first.
+        """
+
+        root_id = self.supply.oldest_ancestor_id(message_id)
+        # Puts the message with the specific id into the cache
+        return self._render_tree(root_id)
+
+    def _expand_upwards_until(self,
+            lines: AttributedLines,
+            ancestor_id: Id,
+            target_upper_offset: int,
+            ) -> Id:
+        """
+        Render trees and prepend them to the AttributedLines until its
+        upper_offset matches or exceeds the target_upper_offset.
+
+        Returns the last tree id that was rendered. If no tree could be
+        rendered, returns the original anchor id.
+
+        Starts at the first older sibling of the ancestor_id (the first sibling
+        above the ancestor_id) and moves upwards sibling by sibling. Does not
+        render the ancestor_id itself.
+        """
+
+        # This loop doesn't use a condition but rather break-s, because I think
+        # it looks cleaner that way. I don't like mixing conditions and breaks
+        # too much, if the conditions are of the same importance.
+        last_rendered_id = ancestor_id
+
+        while True:
+            if lines.upper_offset <= target_upper_offset: break
+
+            next_id = self.supply.previous_id(last_rendered_id)
+            if next_id is None: break
+
+            lines.extend_above(self._render_tree(next_id))
+            last_rendered_id = next_id
+
+        return last_rendered_id
+
+    def _expand_downwards_until(self,
+            lines: AttributedLines,
+            ancestor_id: Id,
+            target_lower_offset: int,
+            ) -> Id:
+        """
+        Render trees and append them to the AttributedLines until its
+        lower_offset matches or exceeds the target_lower_offset.
+
+        Returns the last tree id that was rendered. If no tree could be
+        rendered, returns the original anchor id.
+
+        Starts at the first younger sibling of the ancestor_id (the first
+        sibling below the ancestor_id) and moves downwards sibling by sibling.
+        Does not render the ancestor_id itself.
+        """
+
+        # Almost the same as _expand_upwards_until(), but with small changes.
+        # Maybe these could one day be combined into one function.
+        #
+        # This loop doesn't use a condition but rather break-s, because I think
+        # it looks cleaner that way. I don't like mixing conditions and breaks
+        # too much, if the conditions are of the same importance.
+
+        last_rendered_id = ancestor_id
+
+        while True:
+            if lines.upper_offset >= target_lower_offset: break
+
+            next_id = self.supply.next_id(last_rendered_id)
+            if next_id is None: break
+
+            lines.extend_below(self._draw_tree(next_id))
+            last_rendered_id = next_id
+
+        return last_rendered_id
+
+    # Rendering the screen
+
+    def _render_screen(self) -> AttributedLines:
+        """
+        Render an AttributedLines that fills the screen (as far as possible),
+        taking into account the anchor offset.
+
+        This does NOT fix scrolling (i. e. by min()- or max()-ing the upper and
+        lower offsets). Instead, scrolling should be fixed when the anchor
+        offset is changed or the resolution changes.
+        """
+
+        # TODO maybe extend with an additional offset for scrolling
+
+        lines: AttributedLines
+
+        if self.cursor_id is None:
+            # If the cursor is None, that means that it should always be
+            # displayed at the very bottom of the room. It also means that
+            # _render_subtree() can't render the cursor, because it would be
+            # the root of a message tree.
+
+            if self.anchor_id is None:
+                # Start with the cursor
+                lines = self._render_cursor()
+                lines.upper_offset = self.absolute_anchor_offset
+                # Then expand upwards
+                lowest_root_id = self.supply.lowest_root_id()
+                if lowest_root_id is not None:
+                    self._expand_upwards_until(lines, lowest_root_id, 0)
+            else:
+                # Start with the anchor as usual
+                lines = self._render_tree_containing(self.anchor_id)
+                lines.upper_offset += self.absolute_anchor_offset
+                # And expand until the screen is full
+                self._expand_upwards_until(lines, self.anchor_id, 0)
+                until_id = self._expand_downwards_until(lines, self.anchor_id,
+                        self.height - 1)
+                # After that, draw the cursor below, if necessary
+                lowest_root_id = self.supply.lowest_root_id()
+                if until_id == lowest_root_id:
+                    lines.extend_below(self._render_cursor())
+        else:
+            # In this case, the cursor is automatically rendered correctly by
+            # _render_subtree(), so we actually don't have to do a lot.
+            #
+            # This case is the normal case, and the case I thought of first
+            # when I designed this part.
+
+            working_id: Id
+            if self.anchor_id is None:
+                working_id = self.cursor_id
+            else:
+                working_id = self.anchor_id
+
+            ancestor_id = self.supply.oldest_ancestor_id(working_id)
+            lines = self._render_tree(ancestor_id)
+            lines.upper_offset += self.absolute_anchor_offset
+            self._expand_upwards_until(lines, ancestor_id, 0)
+            self._expand_downwards_until(lines, ancestor_id,
+                    self.height - 1)
+
+        return lines
+
+    # Updating the internal widget
 
     def redraw(self) -> None:
-        pass
+        """
+        Render new lines and draw them (to the internal widget and thus to the
+        screen on the next screen update).
+        """
+
+        lines = self._render_screen()
+        self.lines_widget.set_lines(lines)
+        self._w = self.lines_widget
+        self._invalidate() # Just to make sure this really gets rendered
+
+    # Cursor movement
+
+    # Scrolling