diff --git a/BFR/MainWindow.xaml b/BFR/MainWindow.xaml
index 6dc8cf3..7a67239 100644
--- a/BFR/MainWindow.xaml
+++ b/BFR/MainWindow.xaml
@@ -6,6 +6,7 @@
         mc:Ignorable="d" MinWidth="720" MinHeight="480"
         x:Class="BFR.MainWindow"
         Title="BFR">
+  
   <Grid RowDefinitions="auto,auto,*" ColumnDefinitions="*,*,*" Classes="StyleBorders">
     <!-- Directory Selection + Filters -->
     <Border Grid.Row="0" Grid.ColumnSpan="3">
@@ -17,13 +18,13 @@
         <!-- Filters -->
         <Grid Grid.Row="1" Grid.ColumnSpan="3" ColumnDefinitions="auto,*,auto,*,auto,auto,auto,auto" IsVisible="{Binding #FilterExpander.IsExpanded}">
           <TextBlock Grid.Column="0" Text="Extension:"/>
-          <TextBox Grid.Column="1" Text="{Binding FilterExtension}" KeyUp="FilterChanged"/>
+          <TextBox Grid.Column="1" Text="{Binding FilterExtension}" PropertyChanged="FilterChanged"/>
           <TextBlock Grid.Column="2" Text="Name:"/>
-          <TextBox Grid.Column="3" Text="{Binding FilterPattern}" KeyUp="FilterChanged"/>
+          <TextBox Grid.Column="3" Text="{Binding FilterPattern}" PropertyChanged="FilterChanged"/>
           <TextBlock Grid.Column="4" Text="Full Name:"/>
-          <CheckBox Grid.Column="5" IsChecked="{Binding FilterFullName}" Click="FilterChanged"/>
+          <CheckBox Grid.Column="5" IsChecked="{Binding FilterFullName}" PropertyChanged="FilterChanged"/>
           <TextBlock Grid.Column="6" Text="Regex:"/>
-          <CheckBox Grid.Column="7" IsChecked="{Binding FilterRegex}" Click="FilterChanged" Margin="4,4,5,4"/>
+          <CheckBox Grid.Column="7" IsChecked="{Binding FilterRegex}" PropertyChanged="FilterChanged" Margin="4,4,5,4"/>
         </Grid>
       </Grid>
     </Border>
@@ -99,6 +100,10 @@
       <Setter Property="Margin" Value="4"/>
       <Setter Property="Grid.Column" Value="1"/>
     </Style>
+    <Style Selector="Grid > NumericUpDown">
+      <Setter Property="Margin" Value="4"/>
+      <Setter Property="Grid.Column" Value="1"/>
+    </Style>
     <Style Selector="Grid > CheckBox">
       <Setter Property="Margin" Value="4"/>
       <Setter Property="Grid.Column" Value="1"/>
@@ -151,12 +156,45 @@
       <Expander Classes="OperationExpander">
         <Grid ColumnDefinitions="auto,*" RowDefinitions="*,*">
           <TextBlock Grid.Row="0" Text="Replacement:"/>
-          <TextBox Grid.Row="0" Text="{Binding Replacement}" KeyUp="PreviewChanged"/>
+          <TextBox Grid.Row="0" Text="{Binding Replacement}" PropertyChanged="PreviewChanged"/>
           <TextBlock Grid.Row="1" Text="Full Name:"/>
-          <CheckBox Grid.Row="1" IsChecked="{Binding FullName}" Click="PreviewChanged"/>
+          <CheckBox Grid.Row="1" IsChecked="{Binding FullName}" PropertyChanged="PreviewChanged"/>
+        </Grid>
+      </Expander>
+    </DataTemplate>
+    <DataTemplate DataType="{x:Type ops:Replace}">
+      <Expander Classes="OperationExpander">
+        <Grid ColumnDefinitions="auto,*" RowDefinitions="auto,auto,auto,auto,auto,auto,auto,auto,auto,auto,auto">
+          <TextBlock Grid.Row="0" Text="Mode:"/>
+          <ComboBox Grid.Row="0" Items="{Binding Modes}" SelectedItem="{Binding Mode}" PropertyChanged="PreviewChanged">
+            <ComboBox.ItemTemplate>
+              <DataTemplate>
+                <TextBlock Text="{Binding Name}"/>
+              </DataTemplate>
+            </ComboBox.ItemTemplate>
+          </ComboBox>
+          <TextBlock Grid.Row="1" Text="Pattern:" IsVisible="{Binding Mode.IsPatternMode}"/>
+          <TextBox Grid.Row="1" Text="{Binding Pattern}" IsVisible="{Binding Mode.IsPatternMode}" PropertyChanged="PreviewChanged"/>
+          <TextBlock Grid.Row="2" Text="Characters:" IsVisible="{Binding Mode.IsCharactersMode}"/>
+          <TextBox Grid.Row="2" Text="{Binding Characters}" IsVisible="{Binding Mode.IsCharactersMode}" PropertyChanged="PreviewChanged"/>
+          <TextBlock Grid.Row="3" Text="From N:" IsVisible="{Binding Mode.IsFromNToNMode}"/>
+          <NumericUpDown Grid.Row="3" Value="{Binding FromN}" IsVisible="{Binding Mode.IsFromNToNMode}" PropertyChanged="PreviewChanged"/>
+          <TextBlock Grid.Row="4" Text="To N:" IsVisible="{Binding Mode.IsFromNToNMode}"/>
+          <NumericUpDown Grid.Row="4" Value="{Binding ToN}" IsVisible="{Binding Mode.IsFromNToNMode}" PropertyChanged="PreviewChanged"/>
+          <TextBlock Grid.Row="5" Text="First N:" IsVisible="{Binding Mode.IsFirstNMode}"/>
+          <NumericUpDown Grid.Row="5" Value="{Binding FirstN}" IsVisible="{Binding Mode.IsFirstNMode}" PropertyChanged="PreviewChanged"/>
+          <TextBlock Grid.Row="6" Text="Last N:" IsVisible="{Binding Mode.IsLastNMode}"/>
+          <NumericUpDown Grid.Row="6" Value="{Binding LastN}" IsVisible="{Binding Mode.IsLastNMode}" PropertyChanged="PreviewChanged"/>
+          <TextBlock Grid.Row="7" Text="Replacement:"/>
+          <TextBox Grid.Row="7" Text="{Binding Replacement}" PropertyChanged="PreviewChanged"/>
+          <TextBlock Grid.Row="8" Text="Regex:" IsVisible="{Binding Mode.IsPatternMode}"/>
+          <CheckBox Grid.Row="8" IsChecked="{Binding UseRegex}" IsVisible="{Binding Mode.IsPatternMode}" PropertyChanged="PreviewChanged"/>
+          <TextBlock Grid.Row="9" Text="Replace Regex:" IsVisible="{Binding Mode.IsPatternMode}"/>
+          <CheckBox Grid.Row="9" IsChecked="{Binding UseRegexReplace}" IsVisible="{Binding Mode.IsPatternMode}" PropertyChanged="PreviewChanged"/>
+          <TextBlock Grid.Row="10" Text="Full Name:"/>
+          <CheckBox Grid.Row="10" IsChecked="{Binding FullName}" PropertyChanged="PreviewChanged"/>
         </Grid>
       </Expander>
     </DataTemplate>
   </Window.DataTemplates>
-
 </Window>
diff --git a/BFR/MainWindow.xaml.cs b/BFR/MainWindow.xaml.cs
index 89191cf..bfcb4d1 100644
--- a/BFR/MainWindow.xaml.cs
+++ b/BFR/MainWindow.xaml.cs
@@ -5,10 +5,9 @@ using System.Threading.Tasks;
 using System.Collections.Generic;
 using System.Text.RegularExpressions;
 
-using Avalonia.Input;
+using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
-using Avalonia.Interactivity;
 
 using BFR.Helpers;
 using BFR.DataModels;
@@ -25,22 +24,18 @@ namespace BFR
             Filter();
         }
 
-        public void FilterChanged(object sender, KeyEventArgs e) => Filter();
-        public void FilterChanged(object sender, RoutedEventArgs e) => Filter();
+        public void FilterChanged(object sender, AvaloniaPropertyChangedEventArgs e) => Filter(); // Bind to PropertyChanged
         public void Filter()
         {
             // Filter all files in the directory for those satisfying the given filters
             Files.ReplaceAll(AllFiles.Where(x =>
-                (FilterExtension == "" || x.Extension == FilterExtension)
+                (FilterExtension == "" || x.OldExtension == FilterExtension)
                 && (FilterFullName ? x.OldFullName : x.OldName).RegexContains(FilterRegex ? FilterPattern : Regex.Escape(FilterPattern))));
 
             Preview();
         }
 
-        public void PreviewChanged(object sender, KeyEventArgs e) => Preview();                       // TextBox.KeyUp
-        public void PreviewChanged(object sender, RoutedEventArgs e) => Preview();                    // CheckBox.Click
-        public void PreviewChanged(object sender, SelectionChangedEventArgs e) => Preview();          // ComboBox.SelectionChanged
-        public void PreviewChanged(object sender, NumericUpDownValueChangedEventArgs e) => Preview(); // NumericUpDown.ValueChanged
+        public void PreviewChanged(object sender, AvaloniaPropertyChangedEventArgs e) => Preview(); // Bind to PropertyChanged
         public void Preview()
         {
             // Reset all files to how they currently exist
diff --git a/BFR/MainWindowUIProperties.cs b/BFR/MainWindowUIProperties.cs
index 157b8e8..688f1cc 100644
--- a/BFR/MainWindowUIProperties.cs
+++ b/BFR/MainWindowUIProperties.cs
@@ -1,10 +1,11 @@
-using Avalonia;
+using System.Collections.Generic;
+
+using Avalonia;
 using Avalonia.Collections;
 using Avalonia.Controls;
 
 using BFR.DataModels;
 using BFR.Operations;
-using System.Collections.Generic;
 
 namespace BFR
 {
@@ -22,7 +23,8 @@ namespace BFR
         public int SelectedOperationType { get; set; } = 0;
         public OperationType[] OperationTypes { get; } = new[]
         {
-            OperationType.Make<Overwrite>()
+            OperationType.Make<Overwrite>(),
+            OperationType.Make<Replace>()
         };
 
         public readonly AvaloniaProperty<bool> isCommitButtonEnabled =
diff --git a/BFR/Operations/OperationMode.cs b/BFR/Operations/OperationMode.cs
new file mode 100644
index 0000000..2ba79fb
--- /dev/null
+++ b/BFR/Operations/OperationMode.cs
@@ -0,0 +1,11 @@
+namespace BFR.Operations
+{
+    public class OperationMode
+    {
+        public int Index { get; }
+        public string Name { get; }
+
+        public OperationMode(int index, string name) =>
+            (Index, Name) = (index, name);
+    }
+}
diff --git a/BFR/Operations/Replace.cs b/BFR/Operations/Replace.cs
new file mode 100644
index 0000000..1f7351a
--- /dev/null
+++ b/BFR/Operations/Replace.cs
@@ -0,0 +1,85 @@
+using System;
+using System.Linq;
+using System.Collections.Generic;
+
+using Avalonia;
+
+using BFR.Helpers;
+using BFR.DataModels;
+using System.Text.RegularExpressions;
+
+namespace BFR.Operations
+{
+    public class Replace : Operation
+    {
+        private static readonly ReplaceMode DefaultMode = new ReplaceMode(0, "Pattern");
+
+        public override string Name => "Replace";
+        public override string Description => "Replaces the selected part of the file name.";
+
+        public AvaloniaProperty<ReplaceMode> modeProperty =
+            AvaloniaProperty.Register<MainWindow, ReplaceMode>(nameof(Mode), defaultValue: DefaultMode);
+        public ReplaceMode Mode { get => GetValue(modeProperty); set => SetValue(modeProperty, value); }
+        public ReplaceMode[] Modes { get; } = new ReplaceMode[]
+        {
+            DefaultMode,
+            new ReplaceMode(1, "Characters"),
+            new ReplaceMode(2, "FromNToN"),
+            new ReplaceMode(3, "FirstN"),
+            new ReplaceMode(4, "LastN"),
+        };                 
+
+        public string Replacement { get; set; } = "";
+        public bool FullName { get; set; } = false;
+        public string Pattern { get; set; } = "";
+        public bool UseRegex { get; set; } = false;
+        public bool UseRegexReplace { get; set; } = false;
+        public string Characters { get; set; } = "";
+        public int FirstN { get; set; } = 0;
+        public int LastN { get; set; } = 0;
+        public int FromN { get; set; } = 0;
+        public int ToN { get; set; } = 0;
+
+        protected override void ApplyToInternal(IList<FileModel> files)
+        {
+            // Fail conditions: Various out-of-bounds
+            var shortestLength = files.Min(x => FullName ? x.FullName.Length : x.Name.Length);
+            if (FirstN > shortestLength) throw new OperationException($"First N can't be greater than the shortest file name length ({shortestLength}).");
+            if (LastN > shortestLength) throw new OperationException($"Last N can't be greater than the shortest file name length ({shortestLength}).");
+            if (FromN > shortestLength) throw new OperationException($"From N can't be greater than the shortest file name length ({shortestLength}).");
+            if (ToN > shortestLength) throw new OperationException($"To N can't be greater than the shortest file name length ({shortestLength}).");
+            if (FromN > ToN) throw new OperationException("From N can't be greater than To N.");
+
+            // Regex Failure
+            if(Mode.IsPatternMode && UseRegex)
+                try { "".Replace(Pattern, Replacement, true, false); }
+                catch(Exception) { throw new OperationException("Invalid Regex Pattern."); }
+
+            // Apply operation
+            foreach(var file in files)
+            {
+                var newName = FullName ? file.FullName : file.Name;
+
+                newName = Mode.Index switch
+                {
+                    0 => newName.Replace(Pattern, Replacement, UseRegex, UseRegexReplace),
+                    1 => Characters.Length > 0 ? Regex.Replace(newName, $"[{Characters}]", Replacement.Replace("$", "$$")) : newName,
+                    2 => Regex.Replace(newName, $"^(.{{{FromN}}}).+(.{{{newName.Length - ToN - 1}}})$", $"$1{Replacement.Replace("$", "$$")}$2"),
+                    3 => Regex.Replace(newName, $"^.{{{FirstN}}}", Replacement.Replace("$", "$$")),
+                    4 => Regex.Replace(newName, $".{{{LastN}}}$", Replacement.Replace("$", "$$")),
+                    _ => newName
+                };
+
+                if (FullName) file.FullName = newName;
+                else file.Name = newName;
+            }
+        }
+
+        private string ReplaceAllCharacters(string input, string characters, string replacement)
+        {
+            foreach (var character in characters)
+                input = input.Replace(character.ToString(), replacement);
+            return input;
+        }
+    }
+}
diff --git a/BFR/Operations/ReplaceMode.cs b/BFR/Operations/ReplaceMode.cs
new file mode 100644
index 0000000..b42f7db
--- /dev/null
+++ b/BFR/Operations/ReplaceMode.cs
@@ -0,0 +1,14 @@
+namespace BFR.Operations
+{
+    public class ReplaceMode : OperationMode
+    {
+        public bool IsPatternMode => Index == 0;
+        public bool IsCharactersMode => Index == 1;
+        public bool IsFromNToNMode => Index == 2;
+        public bool IsFirstNMode => Index == 3;
+        public bool IsLastNMode => Index == 4;
+
+        public ReplaceMode(int index, string name) :
+            base(index, name) { }
+    }
+}