diff --git a/docs/changes.txt b/docs/changes.txt
index 4023793277..7e7620bf75 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -446,6 +446,7 @@ All (GUI):
 
 - Added documented, public wxNavigationEnabled<> class.
 - Added wxTextCtrl::PositionToCoords() (Navaneeth).
+- Added support for wxHELP button to wxMessageDialog.
 - Support float, double and file name values in wxGenericValidator (troelsk).
 - Fix keyboard navigation in wxGrid with hidden columns (ivan_14_32).
 - Add wxDataViewEvent::IsEditCancelled() (Allonii).
diff --git a/include/wx/generic/msgdlgg.h b/include/wx/generic/msgdlgg.h
index f6583bd351..21db4aa32b 100644
--- a/include/wx/generic/msgdlgg.h
+++ b/include/wx/generic/msgdlgg.h
@@ -32,6 +32,7 @@ protected:
 
     void OnYes(wxCommandEvent& event);
     void OnNo(wxCommandEvent& event);
+    void OnHelp(wxCommandEvent& event);
     void OnCancel(wxCommandEvent& event);
 
     // can be overridden to provide more contents to the dialog
diff --git a/include/wx/gtk/msgdlg.h b/include/wx/gtk/msgdlg.h
index daab4caac9..8c0a7b095c 100644
--- a/include/wx/gtk/msgdlg.h
+++ b/include/wx/gtk/msgdlg.h
@@ -40,6 +40,7 @@ private:
     virtual wxString GetDefaultNoLabel() const;
     virtual wxString GetDefaultOKLabel() const;
     virtual wxString GetDefaultCancelLabel() const;
+    virtual wxString GetDefaultHelpLabel() const;
 
     // create the real GTK+ dialog: this is done from ShowModal() to allow
     // changing the message between constructing the dialog and showing it
diff --git a/include/wx/msgdlg.h b/include/wx/msgdlg.h
index ca96fc7ff9..c3e8d9af4f 100644
--- a/include/wx/msgdlg.h
+++ b/include/wx/msgdlg.h
@@ -177,10 +177,16 @@ public:
         return true;
     }
 
+    virtual bool SetHelpLabel(const ButtonLabel& help)
+    {
+        DoSetCustomLabel(m_help, help);
+        return true;
+    }
+
     // test if any custom labels were set
     bool HasCustomLabels() const
     {
-        return !(m_ok.empty() && m_cancel.empty() &&
+        return !(m_ok.empty() && m_cancel.empty() && m_help.empty() &&
                  m_yes.empty() && m_no.empty());
     }
 
@@ -195,6 +201,8 @@ public:
         { return m_ok.empty() ? GetDefaultOKLabel() : m_ok; }
     wxString GetCancelLabel() const
         { return m_cancel.empty() ? GetDefaultCancelLabel() : m_cancel; }
+    wxString GetHelpLabel() const
+        { return m_help.empty() ? GetDefaultHelpLabel() : m_help; }
 
     // based on message dialog style, returns exactly one of: wxICON_NONE,
     // wxICON_ERROR, wxICON_WARNING, wxICON_QUESTION, wxICON_INFORMATION
@@ -250,6 +258,7 @@ protected:
     const wxString& GetCustomYesLabel() const { return m_yes; }
     const wxString& GetCustomNoLabel() const { return m_no; }
     const wxString& GetCustomOKLabel() const { return m_ok; }
+    const wxString& GetCustomHelpLabel() const { return m_help; }
     const wxString& GetCustomCancelLabel() const { return m_cancel; }
 
 private:
@@ -259,13 +268,15 @@ private:
     virtual wxString GetDefaultNoLabel() const { return wxGetTranslation("No"); }
     virtual wxString GetDefaultOKLabel() const { return wxGetTranslation("OK"); }
     virtual wxString GetDefaultCancelLabel() const { return wxGetTranslation("Cancel"); }
+    virtual wxString GetDefaultHelpLabel() const { return wxGetTranslation("Help"); }
 
     // labels for the buttons, initially empty meaning that the defaults should
     // be used, use GetYes/No/OK/CancelLabel() to access them
     wxString m_yes,
              m_no,
              m_ok,
-             m_cancel;
+             m_cancel,
+             m_help;
 
     wxDECLARE_NO_COPY_CLASS(wxMessageDialogBase);
 };
diff --git a/include/wx/msw/private/msgdlg.h b/include/wx/msw/private/msgdlg.h
index 5df01fc10d..45db8702e7 100644
--- a/include/wx/msw/private/msgdlg.h
+++ b/include/wx/msw/private/msgdlg.h
@@ -30,8 +30,10 @@ namespace wxMSWMessageDialog
     class wxMSWTaskDialogConfig
     {
     public:
+        enum { MAX_BUTTONS = 4  };
+
         wxMSWTaskDialogConfig()
-            : buttons(new TASKDIALOG_BUTTON[3]),
+            : buttons(new TASKDIALOG_BUTTON[MAX_BUTTONS]),
               parent(NULL),
               iconId(0),
               style(0),
@@ -53,6 +55,7 @@ namespace wxMSWMessageDialog
         wxString btnNoLabel;
         wxString btnOKLabel;
         wxString btnCancelLabel;
+        wxString btnHelpLabel;
 
         // Will create a task dialog with it's paremeters for it's creation
         // stored in the provided TASKDIALOGCONFIG parameter.
diff --git a/include/wx/osx/msgdlg.h b/include/wx/osx/msgdlg.h
index cad3de35b7..9c3d38067d 100644
--- a/include/wx/osx/msgdlg.h
+++ b/include/wx/osx/msgdlg.h
@@ -43,7 +43,7 @@ protected:
     void* ConstructNSAlert();
 #endif
 
-    int m_buttonId[3];
+    int m_buttonId[4];
     int m_buttonCount;
 
 #if wxOSX_USE_COCOA
diff --git a/interface/wx/msgdlg.h b/interface/wx/msgdlg.h
index 0448b04366..70aba8cca1 100644
--- a/interface/wx/msgdlg.h
+++ b/interface/wx/msgdlg.h
@@ -22,6 +22,12 @@
         Puts Yes and No buttons in the message box. It is recommended to always
         use @c wxCANCEL with this style as otherwise the message box won't have
         a close button under wxMSW and the user will be forced to answer it.
+    @style{wxHELP}
+        Puts a Help button to the message box. This button can have special
+        appearance or be specially positioned if its label is not changed from
+        the default one. Notice that using this button is not supported when
+        showing a message box from non-main thread in wxOSX/Cocoa and it is not
+        supported in wxOSX/Carbon at all. @since 2.9.3.
     @style{wxNO_DEFAULT}
         Makes the "No" button default, can only be used with @c wxYES_NO.
     @style{wxCANCEL_DEFAULT}
@@ -116,6 +122,19 @@ public:
     */
     virtual void SetExtendedMessage(const wxString& extendedMessage);
 
+    /**
+        Sets the label for the Help button.
+
+        Please see the remarks in SetYesNoLabels() documentation.
+
+        Notice that changing the label of the help button resets its special
+        status (if any, this depends on the platform) and it will be treated
+        just like another button in this case.
+
+        @since 2.9.3
+     */
+    virtual bool SetHelpLabel(const ButtonLabel& help);
+
     /**
         Sets the message shown by the dialog.
 
@@ -190,7 +209,8 @@ public:
     virtual bool SetYesNoLabels(const ButtonLabel& yes, const ButtonLabel& no);
 
     /**
-        Shows the dialog, returning one of wxID_OK, wxID_CANCEL, wxID_YES, wxID_NO.
+        Shows the dialog, returning one of wxID_OK, wxID_CANCEL, wxID_YES,
+        wxID_NO or wxID_HELP.
 
         Notice that this method returns the identifier of the button which was
         clicked unlike wxMessageBox() function.
@@ -215,9 +235,9 @@ public:
     extended text and custom labels for the message box buttons, are not
     provided by this function but only by wxMessageDialog.
 
-    The return value is one of: @c wxYES, @c wxNO, @c wxCANCEL or @c wxOK
-    (notice that this return value is @b different from the return value of
-    wxMessageDialog::ShowModal()).
+    The return value is one of: @c wxYES, @c wxNO, @c wxCANCEL, @c wxOK or @c
+    wxHELP (notice that this return value is @b different from the return value
+    of wxMessageDialog::ShowModal()).
 
     For example:
     @code
diff --git a/samples/dialogs/dialogs.cpp b/samples/dialogs/dialogs.cpp
index 335cc16ca2..14f1a80318 100644
--- a/samples/dialogs/dialogs.cpp
+++ b/samples/dialogs/dialogs.cpp
@@ -2669,6 +2669,7 @@ const TestMessageBoxDialog::BtnInfo TestMessageBoxDialog::ms_btnInfo[] =
     { wxNO,     "&No"     },
     { wxOK,     "&Ok"     },
     { wxCANCEL, "&Cancel" },
+    { wxHELP,   "&Help"   },
 };
 
 BEGIN_EVENT_TABLE(TestMessageBoxDialog, wxDialog)
@@ -2889,6 +2890,11 @@ void TestMessageBoxDialog::PrepareMessageDialog(wxMessageDialogBase &dlg)
             dlg.SetOKLabel(m_labels[Btn_Ok]->GetValue());
         }
     }
+
+    if ( style & wxHELP )
+    {
+        dlg.SetHelpLabel(m_labels[Btn_Help]->GetValue());
+    }
 }
 
 void TestMessageBoxDialog::OnApply(wxCommandEvent& WXUNUSED(event))
@@ -2896,7 +2902,34 @@ void TestMessageBoxDialog::OnApply(wxCommandEvent& WXUNUSED(event))
     wxMessageDialog dlg(this, GetMessage(), "Test Message Box", GetStyle());
     PrepareMessageDialog(dlg);
 
-    dlg.ShowModal();
+    wxString btnName;
+    switch ( dlg.ShowModal() )
+    {
+        case wxID_OK:
+            btnName = "OK";
+            break;
+
+        case wxID_CANCEL:
+            // Avoid the extra message box if the dialog was cancelled.
+            return;
+
+        case wxID_YES:
+            btnName = "Yes";
+            break;
+
+        case wxID_NO:
+            btnName = "No";
+            break;
+
+        case wxID_HELP:
+            btnName = "Help";
+            break;
+
+        default:
+            btnName = "Unknown";
+    }
+
+    wxLogMessage("Dialog was closed with the \"%s\" button.", btnName);
 }
 
 void TestMessageBoxDialog::OnClose(wxCommandEvent& WXUNUSED(event))
diff --git a/samples/dialogs/dialogs.h b/samples/dialogs/dialogs.h
index fbad49919a..61dd0f85aa 100644
--- a/samples/dialogs/dialogs.h
+++ b/samples/dialogs/dialogs.h
@@ -228,6 +228,7 @@ private:
         Btn_No,
         Btn_Ok,
         Btn_Cancel,
+        Btn_Help,
         Btn_Max
     };
 
diff --git a/src/common/utilscmn.cpp b/src/common/utilscmn.cpp
index 6e9a224e9d..4ff8dade7a 100644
--- a/src/common/utilscmn.cpp
+++ b/src/common/utilscmn.cpp
@@ -1361,6 +1361,8 @@ int wxMessageBox(const wxString& message, const wxString& caption, long style,
             return wxNO;
         case wxID_CANCEL:
             return wxCANCEL;
+        case wxID_HELP:
+            return wxHELP;
     }
 
     wxFAIL_MSG( wxT("unexpected return code from wxMessageDialog") );
diff --git a/src/generic/msgdlgg.cpp b/src/generic/msgdlgg.cpp
index 3fd78a7269..c3dd7a8067 100644
--- a/src/generic/msgdlgg.cpp
+++ b/src/generic/msgdlgg.cpp
@@ -74,6 +74,7 @@ protected:
 BEGIN_EVENT_TABLE(wxGenericMessageDialog, wxDialog)
         EVT_BUTTON(wxID_YES, wxGenericMessageDialog::OnYes)
         EVT_BUTTON(wxID_NO, wxGenericMessageDialog::OnNo)
+        EVT_BUTTON(wxID_HELP, wxGenericMessageDialog::OnHelp)
         EVT_BUTTON(wxID_CANCEL, wxGenericMessageDialog::OnCancel)
 END_EVENT_TABLE()
 
@@ -133,6 +134,13 @@ wxSizer *wxGenericMessageDialog::CreateMsgDlgButtonSizer()
                 btnDef = yes;
         }
 
+        if ( m_dialogStyle & wxHELP )
+        {
+            wxButton * const
+                help = new wxButton(this, wxID_HELP, GetCustomHelpLabel());
+            sizerStd->AddButton(help);
+        }
+
         if ( btnDef )
         {
             btnDef->SetDefault();
@@ -148,7 +156,7 @@ wxSizer *wxGenericMessageDialog::CreateMsgDlgButtonSizer()
     // Use standard labels for all buttons
     return CreateSeparatedButtonSizer
            (
-                m_dialogStyle & (wxOK | wxCANCEL | wxYES_NO |
+                m_dialogStyle & (wxOK | wxCANCEL | wxHELP | wxYES_NO |
                                  wxNO_DEFAULT | wxCANCEL_DEFAULT)
            );
 }
@@ -242,6 +250,11 @@ void wxGenericMessageDialog::OnNo(wxCommandEvent& WXUNUSED(event))
     EndModal( wxID_NO );
 }
 
+void wxGenericMessageDialog::OnHelp(wxCommandEvent& WXUNUSED(event))
+{
+    EndModal( wxID_HELP );
+}
+
 void wxGenericMessageDialog::OnCancel(wxCommandEvent& WXUNUSED(event))
 {
     // Allow cancellation via ESC/Close button except if
diff --git a/src/gtk/msgdlg.cpp b/src/gtk/msgdlg.cpp
index d459602f0b..2b47ac27ef 100644
--- a/src/gtk/msgdlg.cpp
+++ b/src/gtk/msgdlg.cpp
@@ -74,6 +74,11 @@ wxString wxMessageDialog::GetDefaultCancelLabel() const
     return GTK_STOCK_CANCEL;
 }
 
+wxString wxMessageDialog::GetDefaultHelpLabel() const
+{
+    return GTK_STOCK_HELP;
+}
+
 void wxMessageDialog::DoSetCustomLabel(wxString& var, const ButtonLabel& label)
 {
     int stockId = label.GetStockId();
@@ -135,16 +140,21 @@ void wxMessageDialog::GTKCreateMsgDialog()
     // when using custom labels, we have to add all the buttons ourselves
     if ( !HasCustomLabels() )
     {
-        if ( m_dialogStyle & wxYES_NO )
+        // "Help" button is not supported by predefined combinations so we
+        // always need to create the buttons manually when it's used.
+        if ( !(m_dialogStyle & wxHELP) )
         {
-            if ( !(m_dialogStyle & wxCANCEL) )
-                buttons = GTK_BUTTONS_YES_NO;
-            //else: no standard GTK_BUTTONS_YES_NO_CANCEL so leave as NONE
-        }
-        else if ( m_dialogStyle & wxOK )
-        {
-            buttons = m_dialogStyle & wxCANCEL ? GTK_BUTTONS_OK_CANCEL
-                                               : GTK_BUTTONS_OK;
+            if ( m_dialogStyle & wxYES_NO )
+            {
+                if ( !(m_dialogStyle & wxCANCEL) )
+                    buttons = GTK_BUTTONS_YES_NO;
+                //else: no standard GTK_BUTTONS_YES_NO_CANCEL so leave as NONE
+            }
+            else if ( m_dialogStyle & wxOK )
+            {
+                buttons = m_dialogStyle & wxCANCEL ? GTK_BUTTONS_OK_CANCEL
+                                                   : GTK_BUTTONS_OK;
+            }
         }
     }
 
@@ -211,9 +221,16 @@ void wxMessageDialog::GTKCreateMsgDialog()
     const bool addButtons = buttons == GTK_BUTTONS_NONE;
 #endif // wxUSE_LIBHILDON/!wxUSE_LIBHILDON
 
-    if ( m_dialogStyle & wxYES_NO ) // Yes/No or Yes/No/Cancel dialog
+
+    if ( addButtons )
     {
-        if ( addButtons )
+        if ( m_dialogStyle & wxHELP )
+        {
+            gtk_dialog_add_button(dlg, wxGTK_CONV(GetHelpLabel()),
+                                  GTK_RESPONSE_HELP);
+        }
+
+        if ( m_dialogStyle & wxYES_NO ) // Yes/No or Yes/No/Cancel dialog
         {
             // Add the buttons in the correct order which is, according to
             // http://library.gnome.org/devel/hig-book/stable/windows-alert.html.en
@@ -233,32 +250,29 @@ void wxMessageDialog::GTKCreateMsgDialog()
             gtk_dialog_add_button(dlg, wxGTK_CONV(GetYesLabel()),
                                   GTK_RESPONSE_YES);
         }
-
-        // it'd probably be harmless to call gtk_dialog_set_default_response()
-        // twice but why do it if we're going to change the default below
-        // anyhow
-        if ( !(m_dialogStyle & wxCANCEL_DEFAULT) )
+        else // Ok or Ok/Cancel dialog
         {
-            gtk_dialog_set_default_response(dlg,
-                                            m_dialogStyle & wxNO_DEFAULT
-                                                ? GTK_RESPONSE_NO
-                                                : GTK_RESPONSE_YES);
-        }
-    }
-    else if ( addButtons ) // Ok or Ok/Cancel dialog
-    {
-        gtk_dialog_add_button(dlg, wxGTK_CONV(GetOKLabel()), GTK_RESPONSE_OK);
-        if ( m_dialogStyle & wxCANCEL )
-        {
-            gtk_dialog_add_button(dlg, wxGTK_CONV(GetCancelLabel()),
-                                  GTK_RESPONSE_CANCEL);
+            gtk_dialog_add_button(dlg, wxGTK_CONV(GetOKLabel()), GTK_RESPONSE_OK);
+            if ( m_dialogStyle & wxCANCEL )
+            {
+                gtk_dialog_add_button(dlg, wxGTK_CONV(GetCancelLabel()),
+                                      GTK_RESPONSE_CANCEL);
+            }
         }
     }
 
+    gint defaultButton;
     if ( m_dialogStyle & wxCANCEL_DEFAULT )
-    {
-        gtk_dialog_set_default_response(dlg, GTK_RESPONSE_CANCEL);
-    }
+        defaultButton = GTK_RESPONSE_CANCEL;
+    else if ( m_dialogStyle & wxNO_DEFAULT )
+        defaultButton = GTK_RESPONSE_NO;
+    else if ( m_dialogStyle & wxYES_NO )
+        defaultButton = GTK_RESPONSE_YES;
+    else // No need to change the default value, whatever it is.
+        defaultButton = GTK_RESPONSE_NONE;
+
+    if ( defaultButton != GTK_RESPONSE_NONE )
+        gtk_dialog_set_default_response(dlg, defaultButton);
 }
 
 int wxMessageDialog::ShowModal()
@@ -302,6 +316,8 @@ int wxMessageDialog::ShowModal()
             return wxID_YES;
         case GTK_RESPONSE_NO:
             return wxID_NO;
+        case GTK_RESPONSE_HELP:
+            return wxID_HELP;
     }
 }
 
diff --git a/src/msw/msgdlg.cpp b/src/msw/msgdlg.cpp
index 7c786e5141..b0118ae243 100644
--- a/src/msw/msgdlg.cpp
+++ b/src/msw/msgdlg.cpp
@@ -511,6 +511,11 @@ int wxMessageDialog::ShowMessageBox()
         }
     }
 
+    if ( wxStyle & wxHELP )
+    {
+        msStyle |= MB_HELP;
+    }
+
     // set the icon style
     switch ( GetEffectiveIcon() )
     {
@@ -630,7 +635,7 @@ void wxMessageDialog::DoCentre(int dir)
 #ifdef wxHAS_MSW_TASKDIALOG
 
 wxMSWTaskDialogConfig::wxMSWTaskDialogConfig(const wxMessageDialogBase& dlg)
-                     : buttons(new TASKDIALOG_BUTTON[3])
+                     : buttons(new TASKDIALOG_BUTTON[MAX_BUTTONS])
 {
     parent = dlg.GetParentForModalDialog();
     caption = dlg.GetCaption();
@@ -665,6 +670,7 @@ wxMSWTaskDialogConfig::wxMSWTaskDialogConfig(const wxMessageDialogBase& dlg)
     btnNoLabel = dlg.GetNoLabel();
     btnOKLabel = dlg.GetOKLabel();
     btnCancelLabel = dlg.GetCancelLabel();
+    btnHelpLabel = dlg.GetHelpLabel();
 }
 
 void wxMSWTaskDialogConfig::MSWCommonTaskDialogInit(TASKDIALOGCONFIG &tdc)
@@ -755,6 +761,15 @@ void wxMSWTaskDialogConfig::MSWCommonTaskDialogInit(TASKDIALOGCONFIG &tdc)
             AddTaskDialogButton(tdc, IDCANCEL, TDCBF_CANCEL_BUTTON, btnOKLabel);
         }
     }
+
+    if ( style & wxHELP )
+    {
+        // There is no support for "Help" button in the task dialog, it can
+        // only show "Retry" or "Close" ones.
+        useCustomLabels = true;
+
+        AddTaskDialogButton(tdc, IDHELP, 0 /* not used */, btnHelpLabel);
+    }
 }
 
 void wxMSWTaskDialogConfig::AddTaskDialogButton(TASKDIALOGCONFIG &tdc,
@@ -770,6 +785,10 @@ void wxMSWTaskDialogConfig::AddTaskDialogButton(TASKDIALOGCONFIG &tdc,
         tdBtn.nButtonID = btnCustomId;
         tdBtn.pszButtonText = customLabel.wx_str();
         tdc.cButtons++;
+
+        // We should never have more than 4 buttons currently as this is the
+        // maximal number of buttons supported by the message dialog.
+        wxASSERT_MSG( tdc.cButtons <= MAX_BUTTONS, wxT("Too many buttons") );
     }
     else
     {
@@ -839,6 +858,9 @@ int wxMSWMessageDialog::MSWTranslateReturnCode(int msAns)
         case IDNO:
             ans = wxID_NO;
             break;
+        case IDHELP:
+            ans = wxID_HELP;
+            break;
     }
 
     return ans;
diff --git a/src/osx/cocoa/msgdlg.mm b/src/osx/cocoa/msgdlg.mm
index ad44f55600..445a097caa 100644
--- a/src/osx/cocoa/msgdlg.mm
+++ b/src/osx/cocoa/msgdlg.mm
@@ -138,6 +138,8 @@ int wxMessageDialog::ShowModal()
             }
         }
 
+        wxASSERT_MSG( !(style & wxHELP), "wxHELP not supported in non-GUI thread" );
+
         CFOptionFlags exitButton;
         OSStatus err = CFUserNotificationDisplayAlert(
             0, alertType, NULL, NULL, NULL, cfTitle, cfText,
@@ -285,5 +287,15 @@ void* wxMessageDialog::ConstructNSAlert()
         }
 
     }
+
+    if ( style & wxHELP )
+    {
+        wxCFStringRef cfHelpString( GetHelpLabel(), GetFont().GetEncoding() );
+        [alert addButtonWithTitle:cfHelpString.AsNSString()];
+        m_buttonId[ m_buttonCount++ ] = wxID_HELP;
+    }
+
+    wxASSERT_MSG( m_buttonCount <= WXSIZEOF(m_buttonId), "Too many buttons" );
+
     return alert;
 }