diff --git a/src/Discord.Net.Commands/Attributes/GroupAttribute.cs b/src/Discord.Net.Commands/Attributes/GroupAttribute.cs
index a39437862..3521f3f4f 100644
--- a/src/Discord.Net.Commands/Attributes/GroupAttribute.cs
+++ b/src/Discord.Net.Commands/Attributes/GroupAttribute.cs
@@ -5,10 +5,14 @@ namespace Discord.Commands
     [AttributeUsage(AttributeTargets.Class)]
     public class GroupAttribute : Attribute
     {
-        public string Name { get; }
-        public GroupAttribute(string name)
+        public string Prefix { get; }
+        public GroupAttribute()
         {
-            Name = name;
+            Prefix = null;
+        }
+        public GroupAttribute(string prefix)
+        {
+            Prefix = prefix;
         }
     }
 }
diff --git a/src/Discord.Net.Commands/Attributes/ModuleAttribute.cs b/src/Discord.Net.Commands/Attributes/ModuleAttribute.cs
index 5e9481a45..59e6a6aca 100644
--- a/src/Discord.Net.Commands/Attributes/ModuleAttribute.cs
+++ b/src/Discord.Net.Commands/Attributes/ModuleAttribute.cs
@@ -5,5 +5,14 @@ namespace Discord.Commands
     [AttributeUsage(AttributeTargets.Class)]
     public class ModuleAttribute : Attribute
     {
+        public string Prefix { get; }
+        public ModuleAttribute()
+        {
+            Prefix = null;
+        }
+        public ModuleAttribute(string prefix)
+        {
+            Prefix = prefix;
+        }
     }
 }
diff --git a/src/Discord.Net.Commands/Command.cs b/src/Discord.Net.Commands/Command.cs
index d3b94b94c..53c4758d5 100644
--- a/src/Discord.Net.Commands/Command.cs
+++ b/src/Discord.Net.Commands/Command.cs
@@ -19,13 +19,13 @@ namespace Discord.Commands
         public Module Module { get; }
         public IReadOnlyList<CommandParameter> Parameters { get; }
 
-        internal Command(Module module, object instance, CommandAttribute attribute, MethodInfo methodInfo)
+        internal Command(Module module, object instance, CommandAttribute attribute, MethodInfo methodInfo, string groupPrefix)
         {
             Module = module;
             _instance = instance;
 
             Name = methodInfo.Name;
-            Text = attribute.Text;
+            Text = groupPrefix + attribute.Text;
 
             var description = methodInfo.GetCustomAttribute<DescriptionAttribute>();
             if (description != null)
@@ -40,7 +40,7 @@ namespace Discord.Commands
             if (!searchResult.IsSuccess)
                 return ParseResult.FromError(searchResult);
 
-            return await CommandParser.ParseArgs(this, msg, searchResult.ArgText, 0).ConfigureAwait(false);
+            return await CommandParser.ParseArgs(this, msg, searchResult.Text.Substring(Text.Length), 0).ConfigureAwait(false);
         }
         public async Task<ExecuteResult> Execute(IMessage msg, ParseResult parseResult)
         {
diff --git a/src/Discord.Net.Commands/CommandParameter.cs b/src/Discord.Net.Commands/CommandParameter.cs
index 0a5952c48..e5b272ebe 100644
--- a/src/Discord.Net.Commands/CommandParameter.cs
+++ b/src/Discord.Net.Commands/CommandParameter.cs
@@ -18,6 +18,7 @@ namespace Discord.Commands
         public CommandParameter(string name, string description, TypeReader reader, bool isOptional, bool isUnparsed, object defaultValue)
         {
             _reader = reader;
+            Name = name;
             IsOptional = isOptional;
             IsUnparsed = isUnparsed;
             DefaultValue = defaultValue;
diff --git a/src/Discord.Net.Commands/CommandParser.cs b/src/Discord.Net.Commands/CommandParser.cs
index cd23cbbc3..262d3cb58 100644
--- a/src/Discord.Net.Commands/CommandParser.cs
+++ b/src/Discord.Net.Commands/CommandParser.cs
@@ -66,7 +66,7 @@ namespace Discord.Commands
                     else
                     {
                         curParam = command.Parameters.Count > argList.Count ? command.Parameters[argList.Count] : null;
-                        if (curParam.IsUnparsed)
+                        if (curParam != null && curParam.IsUnparsed)
                         {
                             argBuilder.Append(c);
                             continue;
diff --git a/src/Discord.Net.Commands/CommandService.cs b/src/Discord.Net.Commands/CommandService.cs
index a4b4f8679..f3b623700 100644
--- a/src/Discord.Net.Commands/CommandService.cs
+++ b/src/Discord.Net.Commands/CommandService.cs
@@ -15,7 +15,7 @@ namespace Discord.Commands
         private readonly SemaphoreSlim _moduleLock;
         private readonly ConcurrentDictionary<object, Module> _modules;
         private readonly ConcurrentDictionary<string, List<Command>> _map;
-        private readonly Dictionary<Type, TypeReader> _typeReaders;
+        private readonly ConcurrentDictionary<Type, TypeReader> _typeReaders;
 
         public IEnumerable<Module> Modules => _modules.Select(x => x.Value);
         public IEnumerable<Command> Commands => _modules.SelectMany(x => x.Value.Commands);
@@ -25,7 +25,7 @@ namespace Discord.Commands
             _moduleLock = new SemaphoreSlim(1, 1);
             _modules = new ConcurrentDictionary<object, Module>();
             _map = new ConcurrentDictionary<string, List<Command>>();
-            _typeReaders = new Dictionary<Type, TypeReader>
+            _typeReaders = new ConcurrentDictionary<Type, TypeReader>
             {
                 [typeof(string)] = new GenericTypeReader((m, s) => Task.FromResult(TypeReaderResult.FromSuccess(s))),
                 [typeof(byte)] = new GenericTypeReader((m, s) =>
@@ -143,19 +143,20 @@ namespace Discord.Commands
                     throw new ArgumentException($"This module has already been loaded.");
 
                 var typeInfo = moduleInstance.GetType().GetTypeInfo();
-                if (typeInfo.GetCustomAttribute<ModuleAttribute>() == null)
+                var moduleAttr = typeInfo.GetCustomAttribute<ModuleAttribute>();
+                if (moduleAttr != null)
                     throw new ArgumentException($"Modules must be marked with ModuleAttribute.");
 
-                return LoadInternal(moduleInstance, typeInfo);
+                return LoadInternal(moduleInstance, moduleAttr, typeInfo);
             }
             finally
             {
                 _moduleLock.Release();
             }
         }
-        private Module LoadInternal(object moduleInstance, TypeInfo typeInfo)
+        private Module LoadInternal(object moduleInstance, ModuleAttribute moduleAttr, TypeInfo typeInfo)
         {
-            var loadedModule = new Module(this, moduleInstance, typeInfo);
+            var loadedModule = new Module(this, moduleInstance, moduleAttr, typeInfo);
             _modules[moduleInstance] = loadedModule;
 
             foreach (var cmd in loadedModule.Commands)
@@ -176,10 +177,11 @@ namespace Discord.Commands
                 foreach (var type in assembly.ExportedTypes)
                 {
                     var typeInfo = type.GetTypeInfo();
-                    if (typeInfo.GetCustomAttribute<ModuleAttribute>() != null)
+                    var moduleAttr = typeInfo.GetCustomAttribute<ModuleAttribute>();
+                    if (moduleAttr != null)
                     {
                         var moduleInstance = ReflectionUtils.CreateObject(typeInfo);
-                        modules.Add(LoadInternal(moduleInstance, typeInfo));
+                        modules.Add(LoadInternal(moduleInstance, moduleAttr, typeInfo));
                     }
                 }
                 return modules.ToImmutable();
@@ -239,30 +241,34 @@ namespace Discord.Commands
         {
             string lowerInput = input.ToLowerInvariant();
 
-            List<Command> bestGroup = null, group;
-            int startPos = 0, endPos;
+            ImmutableArray<Command>.Builder matches = null;
+            List<Command> group;
+            int pos = -1;
 
             while (true)
             {
-                endPos = input.IndexOf(' ', startPos);
-                string cmdText = endPos == -1 ? input.Substring(startPos) : input.Substring(startPos, endPos - startPos);
+                pos = input.IndexOf(' ', pos + 1);
+                string cmdText = pos == -1 ? input : input.Substring(0, pos);
                 if (!_map.TryGetValue(cmdText, out group))
                     break;
-                bestGroup = group;
-                if (endPos == -1)
+
+                lock (group)
+                {
+                    if (matches == null)
+                        matches = ImmutableArray.CreateBuilder<Command>(group.Count);
+                    for (int i = 0; i < group.Count; i++)
+                        matches.Add(group[i]);
+                }
+
+                if (pos == -1)
                 {
-                    startPos = input.Length;
+                    pos = input.Length;
                     break;
                 }
-                else
-                    startPos = endPos + 1;
             }
             
-            if (bestGroup != null)
-            {
-                lock (bestGroup)
-                    return SearchResult.FromSuccess(bestGroup.ToImmutableArray(), input.Substring(startPos));
-            }
+            if (matches != null)
+                return SearchResult.FromSuccess(input, matches.ToImmutable());
             else
                 return SearchResult.FromError(CommandError.UnknownCommand, "Unknown command.");
         }
@@ -275,7 +281,7 @@ namespace Discord.Commands
                 return searchResult;
 
             var commands = searchResult.Commands;
-            for (int i = 0; i < commands.Count; i++)
+            for (int i = commands.Count - 1; i >= 0; i++)
             {
                 var parseResult = await commands[i].Parse(message, searchResult);
                 if (!parseResult.IsSuccess)
diff --git a/src/Discord.Net.Commands/Extensions/MessageExtensions.cs b/src/Discord.Net.Commands/Extensions/MessageExtensions.cs
index 2ba4973fe..b2e3e173c 100644
--- a/src/Discord.Net.Commands/Extensions/MessageExtensions.cs
+++ b/src/Discord.Net.Commands/Extensions/MessageExtensions.cs
@@ -15,7 +15,7 @@
         public static bool HasStringPrefix(this IMessage msg, string str, ref int argPos)
         {
             var text = msg.RawText;
-            str = str + ' ';
+            //str = str + ' ';
             if (text.StartsWith(str))
             {
                 argPos = str.Length;
diff --git a/src/Discord.Net.Commands/Module.cs b/src/Discord.Net.Commands/Module.cs
index 0f7edb551..ea6e29c28 100644
--- a/src/Discord.Net.Commands/Module.cs
+++ b/src/Discord.Net.Commands/Module.cs
@@ -12,29 +12,39 @@ namespace Discord.Commands
         public IEnumerable<Command> Commands { get; }
         internal object Instance { get; }
 
-        internal Module(CommandService service, object instance, TypeInfo typeInfo)
+        internal Module(CommandService service, object instance, ModuleAttribute moduleAttr, TypeInfo typeInfo)
         {
             Service = service;
             Name = typeInfo.Name;
             Instance = instance;
 
             List<Command> commands = new List<Command>();
-            SearchClass(instance, commands, typeInfo);
+            SearchClass(instance, commands, typeInfo, moduleAttr.Prefix ?? "");
             Commands = commands;
         }
 
-        private void SearchClass(object instance, List<Command> commands, TypeInfo typeInfo)
+        private void SearchClass(object instance, List<Command> commands, TypeInfo typeInfo, string groupPrefix)
         {
+            if (groupPrefix != "")
+                groupPrefix += " ";
             foreach (var method in typeInfo.DeclaredMethods)
             {
                 var cmdAttr = method.GetCustomAttribute<CommandAttribute>();
                 if (cmdAttr != null)
-                    commands.Add(new Command(this, instance, cmdAttr, method));
+                    commands.Add(new Command(this, instance, cmdAttr, method, groupPrefix));
             }
             foreach (var type in typeInfo.DeclaredNestedTypes)
             {
-                if (type.GetCustomAttribute<GroupAttribute>() != null)
-                    SearchClass(ReflectionUtils.CreateObject(type), commands, type);
+                var groupAttrib = type.GetCustomAttribute<GroupAttribute>();
+                if (groupAttrib != null)
+                {
+                    string nextGroupPrefix;
+                    if (groupAttrib.Prefix != null)
+                        nextGroupPrefix = groupPrefix + groupAttrib.Prefix ?? type.Name;
+                    else
+                        nextGroupPrefix = groupPrefix;
+                    SearchClass(ReflectionUtils.CreateObject(type), commands, type, nextGroupPrefix);
+                }
             }
         }
 
diff --git a/src/Discord.Net.Commands/Results/SearchResult.cs b/src/Discord.Net.Commands/Results/SearchResult.cs
index 0c7d671e3..3cda94ba4 100644
--- a/src/Discord.Net.Commands/Results/SearchResult.cs
+++ b/src/Discord.Net.Commands/Results/SearchResult.cs
@@ -6,24 +6,24 @@ namespace Discord.Commands
     [DebuggerDisplay(@"{DebuggerDisplay,nq}")]
     public struct SearchResult : IResult
     {
+        public string Text { get; }
         public IReadOnlyList<Command> Commands { get; }
-        public string ArgText { get; }        
 
         public CommandError? Error { get; }
         public string ErrorReason { get; }
 
         public bool IsSuccess => !Error.HasValue;
 
-        private SearchResult(IReadOnlyList<Command> commands, string argText, CommandError? error, string errorReason)
+        private SearchResult(string text, IReadOnlyList<Command> commands, CommandError? error, string errorReason)
         {
+            Text = text;
             Commands = commands;
-            ArgText = argText;
             Error = error;
             ErrorReason = errorReason;
         }
 
-        internal static SearchResult FromSuccess(IReadOnlyList<Command> commands, string argText)
-            => new SearchResult(commands, argText, null, null);
+        internal static SearchResult FromSuccess(string text, IReadOnlyList<Command> commands)
+            => new SearchResult(text, commands, null, null);
         internal static SearchResult FromError(CommandError error, string reason)
             => new SearchResult(null, null, error, reason);