// In the PageControl's OnMouseDown event handler: 

procedure TForm1.PageControl1MouseDown(Sender: TObject; 
  Button: TMouseButton; Shift: TShiftState; X, Y: Integer); 
begin 
  PageControl1.BeginDrag(False); 
end; 


// In the PageControl's OnDragDrop event handler: 

procedure TForm1.PageControl1DragDrop(Sender, Source: TObject; X, Y: Integer); 
const 
  TCM_GETITEMRECT = $130A; 
var 
  i: Integer; 
  r: TRect; 
begin 
  if not (Sender is TPageControl) then Exit; 
  with PageControl1 do 
  begin 
    for i := 0 to PageCount - 1 do 
    begin 
      Perform(TCM_GETITEMRECT, i, lParam(@r)); 
      if PtInRect(r, Point(X, Y)) then 
      begin 
        if i <> ActivePage.PageIndex then 
          ActivePage.PageIndex := i; 
        Exit; 
      end; 
    end; 
  end; 
end; 

// In the PageControl's OnDragOver event handler: 

procedure TForm1.PageControl1DragOver(Sender, Source: TObject; X, 
  Y: Integer; State: TDragState; var Accept: Boolean); 
begin 
  if Sender is TPageControl then 
    Accept := True; 
end;