diff --git a/src/Decho/ViewModels/AutocompleteController.cs b/src/Decho/ViewModels/AutocompleteController.cs
new file mode 100644
index 0000000..8db20e6
--- /dev/null
+++ b/src/Decho/ViewModels/AutocompleteController.cs
@@ -0,0 +1,103 @@
+using System.Collections.ObjectModel;
+using System.Text.RegularExpressions;
+
+namespace Decho.ViewModels;
+
+public sealed class AutocompleteController : ViewModelBase
+{
+    private readonly List<AutocompleteProvider> _providers;
+
+    private static readonly Regex TriggerPattern = new(@"([@#])(\w*)$", RegexOptions.Compiled);
+
+    public ObservableCollection<string> FilteredItems { get; } = [];
+
+    public bool ShowPopup
+    {
+        get => field;
+        set => this.RaiseAndSetIfChanged(ref field, value);
+    }
+
+    public int SelectedIndex
+    {
+        get => field;
+        set => this.RaiseAndSetIfChanged(ref field, value);
+    }
+
+    public string FilterText
+    {
+        get => field;
+        set => this.RaiseAndSetIfChanged(ref field, value);
+    }
+
+    public AutocompleteProvider? ActiveProvider { get; private set; }
+
+    public int TriggerCharIndex { get; private set; }
+
+    public AutocompleteController(IEnumerable<AutocompleteProvider> providers)
+    {
+        _providers = providers.ToList();
+    }
+
+    public void Update(string text)
+    {
+        if (string.IsNullOrEmpty(text) || _providers.Count == 0)
+        {
+            Reset();
+            return;
+        }
+
+        Match match = TriggerPattern.Match(text);
+        if (!match.Success)
+        {
+            Reset();
+            return;
+        }
+
+        char trigger = match.Groups[1].Value[0];
+        AutocompleteProvider? provider = _providers.FirstOrDefault(p => p.Trigger == trigger);
+        if (provider is null)
+        {
+            Reset();
+            return;
+        }
+
+        string filter = match.Groups[2].Value;
+        ActiveProvider = provider;
+        FilterText = filter;
+        TriggerCharIndex = match.Index;
+
+        List<string> items = provider.ItemsSource().ToList();
+        List<string> filtered = items
+            .Where(item => provider.Filter(item, filter))
+            .Take(provider.MaxResults)
+            .ToList();
+
+        SelectedIndex = -1;
+        FilteredItems.Clear();
+        foreach (string item in filtered)
+        {
+            FilteredItems.Add(item);
+        }
+
+        ShowPopup = FilteredItems.Count > 0;
+        SelectedIndex = 0;
+    }
+
+    public string? GetInsertion(string item)
+    {
+        if (ActiveProvider is null)
+        {
+            return null;
+        }
+
+        return ActiveProvider.FormatInsertion(item);
+    }
+
+    public void Reset()
+    {
+        ShowPopup = false;
+        ActiveProvider = null;
+        FilterText = string.Empty;
+        FilteredItems.Clear();
+    }
+}
\ No newline at end of file
diff --git a/src/Decho/ViewModels/AutocompleteProvider.cs b/src/Decho/ViewModels/AutocompleteProvider.cs
new file mode 100644
index 0000000..a1d8681
--- /dev/null
+++ b/src/Decho/ViewModels/AutocompleteProvider.cs
@@ -0,0 +1,23 @@
+namespace Decho.ViewModels;
+
+public sealed class AutocompleteProvider
+{
+    public char Trigger { get; }
+    public Func<IEnumerable<string>> ItemsSource { get; }
+    public Func<string, string, bool> Filter { get; }
+    public Func<string, string> FormatInsertion { get; }
+    public int MaxResults { get; }
+
+    public AutocompleteProvider(
+        char trigger,
+        Func<IEnumerable<string>> itemsSource,
+        string insertPrefix,
+        int maxResults = 10)
+    {
+        Trigger = trigger;
+        ItemsSource = itemsSource;
+        Filter = (item, filter) => item.StartsWith(filter, StringComparison.OrdinalIgnoreCase);
+        FormatInsertion = item => $"{insertPrefix}{item} ";
+        MaxResults = maxResults;
+    }
+}
\ No newline at end of file
diff --git a/src/Decho/ViewModels/ChatViewModel.cs b/src/Decho/ViewModels/ChatViewModel.cs
index b18b2d0..3a2869f 100644
--- a/src/Decho/ViewModels/ChatViewModel.cs
+++ b/src/Decho/ViewModels/ChatViewModel.cs
@@ -110,6 +110,7 @@ public sealed class ChatViewModel : ViewModelBase
         }
         OnlineUserCount = $"{users.Count}";
         ShowOnlineUsers = true;
+        Composer.UpdateAvailableUsers(OnlineUsers);
     }
 
     public void AddOnlineUser(UserPresenceDto user)
@@ -120,6 +121,7 @@ public sealed class ChatViewModel : ViewModelBase
             OnlineUserCount = $"{OnlineUsers.Count}";
         }
         ShowOnlineUsers = OnlineUsers.Count > 0;
+        Composer.UpdateAvailableUsers(OnlineUsers);
     }
 
     public void RemoveOnlineUser(string username)
@@ -131,6 +133,7 @@ public sealed class ChatViewModel : ViewModelBase
             OnlineUserCount = $"{OnlineUsers.Count}";
         }
         ShowOnlineUsers = OnlineUsers.Count > 0;
+        Composer.UpdateAvailableUsers(OnlineUsers);
     }
 
     public void ClearMessages()
diff --git a/src/Decho/ViewModels/MainWindowViewModel.cs b/src/Decho/ViewModels/MainWindowViewModel.cs
index 4b4fb2e..1bcb437 100644
--- a/src/Decho/ViewModels/MainWindowViewModel.cs
+++ b/src/Decho/ViewModels/MainWindowViewModel.cs
@@ -827,6 +827,12 @@ public sealed class MainWindowViewModel : ViewModelBase
         bool isServerConnected = Sidebar.GetServer(serverUrl)?.IsConnected ?? false;
         Chat.SetChannel(channel, serverUrl, isServerConnected);
 
+        ServerViewModel? currentServer = Sidebar.GetServer(serverUrl);
+        if (currentServer is not null)
+        {
+            Chat.Composer.UpdateAvailableChannels(currentServer.Channels.Select(c => c.Name));
+        }
+
         if (!string.IsNullOrEmpty(serverUrl))
         {
             Chat.Composer.SetCommandHandler(new CommandHandler());
diff --git a/src/Decho/ViewModels/MessageComposerViewModel.cs b/src/Decho/ViewModels/MessageComposerViewModel.cs
index a526956..cd54a43 100644
--- a/src/Decho/ViewModels/MessageComposerViewModel.cs
+++ b/src/Decho/ViewModels/MessageComposerViewModel.cs
@@ -1,5 +1,6 @@
 using EchoHub.Client.Commands;
 
+using System.Collections.ObjectModel;
 using System.Reactive;
 
 namespace Decho.ViewModels;
@@ -14,6 +15,9 @@ public sealed class MessageComposerViewModel : ViewModelBase
 
     private CommandHandler? _commandHandler;
 
+    private readonly ObservableCollection<UserViewModel> _onlineUsers = [];
+    private readonly ObservableCollection<string> _channelNames = [];
+
     public string Draft
     {
         get;
@@ -32,10 +36,44 @@ public sealed class MessageComposerViewModel : ViewModelBase
 
     public bool HasCommandHandler => _commandHandler is not null;
 
+    public AutocompleteController Autocomplete { get; }
+
     public MessageComposerViewModel()
     {
+        AutocompleteProvider mentionProvider = new(
+            trigger: '@',
+            itemsSource: () => _onlineUsers.Select(u => u.Username),
+            insertPrefix: "@");
+
+        AutocompleteProvider channelProvider = new(
+            trigger: '#',
+            itemsSource: () => _channelNames,
+            insertPrefix: "#");
+
+        Autocomplete = new AutocompleteController([mentionProvider, channelProvider]);
+
         IObservable<bool> canSend = this.WhenAnyValue(x => x.Draft, draft => !string.IsNullOrWhiteSpace(draft));
         SendCommand = ReactiveCommand.Create(Send, canSend);
+
+        _ = this.WhenAnyValue(x => x.Draft).Subscribe(OnDraftChanged);
+    }
+
+    public void UpdateAvailableUsers(IEnumerable<UserViewModel> users)
+    {
+        _onlineUsers.Clear();
+        foreach (UserViewModel user in users)
+        {
+            _onlineUsers.Add(user);
+        }
+    }
+
+    public void UpdateAvailableChannels(IEnumerable<string> channelNames)
+    {
+        _channelNames.Clear();
+        foreach (string name in channelNames)
+        {
+            _channelNames.Add(name);
+        }
     }
 
     public void RequestFileUpload(string filePath)
@@ -63,6 +101,24 @@ public sealed class MessageComposerViewModel : ViewModelBase
         return _commandHandler?.IsCommand(input) ?? input.StartsWith('/');
     }
 
+    public void InsertAutocomplete(string item)
+    {
+        string? insertion = Autocomplete.GetInsertion(item);
+        if (insertion is null)
+        {
+            return;
+        }
+
+        string before = Draft[..Autocomplete.TriggerCharIndex];
+        Draft = $"{before}{insertion}";
+        Autocomplete.Reset();
+    }
+
+    private void OnDraftChanged(string? draft)
+    {
+        Autocomplete.Update(draft ?? string.Empty);
+    }
+
     private void Send()
     {
         string text = Draft.Trim();
diff --git a/src/Decho/Views/MessageComposerView.axaml b/src/Decho/Views/MessageComposerView.axaml
index 7a638a0..fb5e191 100644
--- a/src/Decho/Views/MessageComposerView.axaml
+++ b/src/Decho/Views/MessageComposerView.axaml
@@ -4,16 +4,52 @@
              xmlns:i="https://github.com/projektanker/icons.avalonia"
              x:Class="Decho.Views.MessageComposerView"
              x:DataType="vm:MessageComposerViewModel">
-    <Grid ColumnDefinitions="*, Auto, Auto" Margin="5">
-        <TextBox Grid.Column="0"
-                 HorizontalAlignment="Stretch"
-                 Margin="0 0 5 0"
-                 Text="{Binding Draft, Mode=TwoWay}"
-                 IsEnabled="{Binding IsConnected}">
-            <TextBox.KeyBindings>
-                <KeyBinding Command="{Binding SendCommand}" Gesture="Enter" />
-            </TextBox.KeyBindings>
-        </TextBox>
+    <Grid>
+        <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="*" />
+            <ColumnDefinition Width="Auto" />
+            <ColumnDefinition Width="Auto" />
+        </Grid.ColumnDefinitions>
+        <Grid>
+            <TextBox x:Name="MessageTextBox"
+                     HorizontalAlignment="Stretch"
+                     Margin="0 0 5 0"
+                     Text="{Binding Draft, Mode=TwoWay}"
+                     IsEnabled="{Binding IsConnected}"
+                     KeyDown="OnTextBoxKeyDown">
+                <TextBox.KeyBindings>
+                    <KeyBinding Command="{Binding SendCommand}" Gesture="Enter" />
+                </TextBox.KeyBindings>
+            </TextBox>
+            <Popup x:Name="MentionPopup"
+                   Placement="TopEdgeAlignedLeft"
+                   PlacementTarget="{Binding #MessageTextBox}"
+                   IsOpen="{Binding Autocomplete.ShowPopup}"
+                   IsLightDismissEnabled="True"
+                   MinWidth="100"
+                   MaxHeight="140">
+                <ListBox ItemsSource="{Binding Autocomplete.FilteredItems}"
+                         SelectedIndex="{Binding Autocomplete.SelectedIndex}"
+                         BorderThickness="1"
+                         BorderBrush="{DynamicResource UiTheme08}"
+                         Background="{DynamicResource UiTheme02}">
+                    <ListBox.Styles>
+                        <Style Selector="ListBoxItem:selected">
+                            <Setter Property="Background" Value="#3D3D3D" />
+                        </Style>
+                    </ListBox.Styles>
+                    <ListBox.ItemTemplate>
+                        <DataTemplate x:DataType="x:String">
+                            <TextBlock Text="{Binding}"
+                                       FontSize="12"
+                                       Padding="4 2"
+                                       Cursor="Hand"
+                                       PointerPressed="OnMentionPointerPressed" />
+                        </DataTemplate>
+                    </ListBox.ItemTemplate>
+                </ListBox>
+            </Popup>
+        </Grid>
         <Button Grid.Column="1"
                 Height="33"
                 Width="33"
diff --git a/src/Decho/Views/MessageComposerView.axaml.cs b/src/Decho/Views/MessageComposerView.axaml.cs
index 2a6bc25..295cdce 100644
--- a/src/Decho/Views/MessageComposerView.axaml.cs
+++ b/src/Decho/Views/MessageComposerView.axaml.cs
@@ -1,10 +1,13 @@
 using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Interactivity;
+using Avalonia.Media;
 using Avalonia.Platform.Storage;
 
 using Decho.ViewModels;
 
+using System.Globalization;
+
 namespace Decho.Views;
 
 public partial class MessageComposerView : UserControl
@@ -15,6 +18,104 @@ public partial class MessageComposerView : UserControl
         AddHandler(DragDrop.DragOverEvent, OnDragOver);
         AddHandler(DragDrop.DropEvent, OnDrop);
         DragDrop.SetAllowDrop(this, true);
+        DataContextChanged += OnDataContextChanged;
+    }
+
+    private void OnDataContextChanged(object? sender, EventArgs e)
+    {
+        if (DataContext is MessageComposerViewModel vm)
+        {
+            vm.Autocomplete.PropertyChanged += (_, args) =>
+            {
+                if (args.PropertyName is nameof(AutocompleteController.ShowPopup) or nameof(AutocompleteController.FilterText))
+                {
+                    PositionPopupAtCursor();
+                }
+            };
+        }
+    }
+
+    private void OnTextBoxKeyDown(object? sender, KeyEventArgs e)
+    {
+        MessageComposerViewModel? vm = this.GetDataContext<MessageComposerViewModel>();
+        if (vm is null || !vm.Autocomplete.ShowPopup)
+        {
+            return;
+        }
+
+        if (e.Key == Key.Down)
+        {
+            vm.Autocomplete.SelectedIndex = Math.Min(vm.Autocomplete.SelectedIndex + 1, vm.Autocomplete.FilteredItems.Count - 1);
+            e.Handled = true;
+        }
+        else if (e.Key == Key.Up)
+        {
+            vm.Autocomplete.SelectedIndex = Math.Max(vm.Autocomplete.SelectedIndex - 1, 0);
+            e.Handled = true;
+        }
+        else if (e.Key is Key.Enter or Key.Tab)
+        {
+            if (vm.Autocomplete.SelectedIndex >= 0 && vm.Autocomplete.SelectedIndex < vm.Autocomplete.FilteredItems.Count)
+            {
+                InsertAutocomplete(vm.Autocomplete.FilteredItems[vm.Autocomplete.SelectedIndex]);
+                e.Handled = true;
+            }
+        }
+        else if (e.Key == Key.Escape)
+        {
+            vm.Autocomplete.ShowPopup = false;
+            e.Handled = true;
+        }
+    }
+
+    private void OnMentionPointerPressed(object? sender, PointerPressedEventArgs e)
+    {
+        if (sender is TextBlock textBlock && textBlock.DataContext is string item)
+        {
+            InsertAutocomplete(item);
+        }
+    }
+
+    private void InsertAutocomplete(string item)
+    {
+        MessageComposerViewModel? vm = this.GetDataContext<MessageComposerViewModel>();
+        if (vm is null)
+        {
+            return;
+        }
+
+        vm.InsertAutocomplete(item);
+        MessageTextBox.CaretIndex = MessageTextBox.Text?.Length ?? 0;
+        _ = MessageTextBox.Focus();
+    }
+
+    private void PositionPopupAtCursor()
+    {
+        MessageComposerViewModel? vm = this.GetDataContext<MessageComposerViewModel>();
+        if (vm is null)
+        {
+            return;
+        }
+
+        string text = MessageTextBox.Text ?? "";
+        int targetIndex = Math.Min(vm.Autocomplete.TriggerCharIndex, text.Length);
+        string beforeTarget = text[..targetIndex];
+
+        double width = 0;
+        if (beforeTarget.Length > 0)
+        {
+            FormattedText formatted = new(
+                beforeTarget,
+                CultureInfo.CurrentCulture,
+                FlowDirection.LeftToRight,
+                new Typeface(MessageTextBox.FontFamily, MessageTextBox.FontStyle, MessageTextBox.FontWeight, MessageTextBox.FontStretch),
+                MessageTextBox.FontSize,
+                null);
+            width = formatted.Width;
+        }
+
+        double maxOffset = Math.Max(0, MessageTextBox.Bounds.Width - 20);
+        MentionPopup.HorizontalOffset = Math.Min(width + 4, maxOffset);
     }
 
     private async void OnFileUploadClicked(object? sender, RoutedEventArgs e)
diff --git a/src/Decho/Views/MessageItemView.axaml b/src/Decho/Views/MessageItemView.axaml
index 1b23d99..1d4e5a9 100644
--- a/src/Decho/Views/MessageItemView.axaml
+++ b/src/Decho/Views/MessageItemView.axaml
@@ -23,8 +23,8 @@
 						   FontSize="10"
 						   Margin="5 0 0 0" />
 			</StackPanel>
-			<TextBlock VerticalAlignment="Top"
-					   Text="{Binding Content}"
+			<TextBlock x:Name="MessageContent"
+					   VerticalAlignment="Top"
 					   TextWrapping="Wrap"
 					   IsVisible="{Binding ShowContent}" />
 			<Image x:Name="MessageImage"
diff --git a/src/Decho/Views/MessageItemView.axaml.cs b/src/Decho/Views/MessageItemView.axaml.cs
index 4f9e771..0ebc439 100644
--- a/src/Decho/Views/MessageItemView.axaml.cs
+++ b/src/Decho/Views/MessageItemView.axaml.cs
@@ -1,5 +1,7 @@
 using Avalonia.Controls;
+using Avalonia.Controls.Documents;
 using Avalonia.Interactivity;
+using Avalonia.Media;
 using Avalonia.Media.Imaging;
 using Avalonia.Platform.Storage;
 
@@ -7,6 +9,8 @@ using Decho.ViewModels;
 
 using EchoHub.Core.DTOs;
 
+using System.Text.RegularExpressions;
+
 namespace Decho.Views;
 
 public partial class MessageItemView : UserControl
@@ -21,6 +25,8 @@ public partial class MessageItemView : UserControl
         Loaded += OnLoaded;
     }
 
+    private static readonly Regex MentionRegex = new(@"@(\w+)", RegexOptions.Compiled);
+
     private void OnDataContextChanged(object? sender, EventArgs args)
     {
         if (DataContext is MessageViewModel newMsg && newMsg.Model.Id == _loadedMessageId)
@@ -32,6 +38,44 @@ public partial class MessageItemView : UserControl
         _loadCts = new CancellationTokenSource();
         this.FindControl<Image>("MessageImage")?.ClearValue(Image.SourceProperty);
         _loadedMessageId = null;
+
+        if (DataContext is MessageViewModel msg)
+        {
+            BuildMessageInlines(msg.Content);
+        }
+    }
+
+    private void BuildMessageInlines(string content)
+    {
+        TextBlock? tb = MessageContent;
+        if (tb is null)
+        {
+            return;
+        }
+
+        tb.Inlines?.Clear();
+
+        int lastIndex = 0;
+        foreach (Match match in MentionRegex.Matches(content))
+        {
+            if (match.Index > lastIndex)
+            {
+                tb.Inlines?.Add(new Run(content[lastIndex..match.Index]));
+            }
+
+            tb.Inlines?.Add(new Run(match.Value)
+            {
+                Foreground = new SolidColorBrush(Color.Parse("#FEE75C")),
+                FontWeight = FontWeight.Bold,
+            });
+
+            lastIndex = match.Index + match.Length;
+        }
+
+        if (lastIndex < content.Length)
+        {
+            tb.Inlines?.Add(new Run(content[lastIndex..]));
+        }
     }
 
     private void OnLoaded(object? sender, RoutedEventArgs e)
diff --git a/src/EchoHub b/src/EchoHub
index aae7880..b62729d 160000
--- a/src/EchoHub
+++ b/src/EchoHub
@@ -1 +1 @@
-Subproject commit aae788028eaca52a32ef69c1ed4d7939086cec46
+Subproject commit b62729dc95f0eabf18e6b0cc747d4eb4878a6090