diff --git a/MdePkg/Include/IndustryStandard/Usb.h b/MdePkg/Include/IndustryStandard/Usb.h
index ef4acc8999..0d6da311f6 100644
--- a/MdePkg/Include/IndustryStandard/Usb.h
+++ b/MdePkg/Include/IndustryStandard/Usb.h
@@ -170,6 +170,7 @@ typedef enum {
   USB_DESC_TYPE_INTERFACE = 0x04,
   USB_DESC_TYPE_ENDPOINT  = 0x05,
   USB_DESC_TYPE_HID       = 0x21,
+  USB_DESC_TYPE_REPORT    = 0x22,
 
   //
   // Features to be cleared by CLEAR_FEATURE requests
@@ -198,6 +199,17 @@ typedef enum {
 // HID constants definition, see HID rev1.0
 //
 
+//
+// HID standard GET_DESCRIPTOR request.
+//
+#define USB_HID_GET_DESCRIPTOR_REQ_TYPE  0x81
+
+//
+// HID specific requests.
+//
+#define USB_HID_CLASS_GET_REQ_TYPE       0xa1
+#define USB_HID_CLASS_SET_REQ_TYPE       0x21
+
 //
 // HID report item format
 //
diff --git a/MdePkg/Library/UefiUsbLib/Hid.c b/MdePkg/Library/UefiUsbLib/Hid.c
index 3a62d523f1..ad2c158401 100644
--- a/MdePkg/Library/UefiUsbLib/Hid.c
+++ b/MdePkg/Library/UefiUsbLib/Hid.c
@@ -1,6 +1,7 @@
 /** @file
 
-  The library provides USB descriptor, protocol operations.
+  The library provides USB HID Class standard and specific requests defined
+  in USB HID Firmware Specification 7 section : Requests.
   
   Copyright (c) 2004, Intel Corporation
   All rights reserved. This program and the accompanying materials
@@ -15,6 +16,18 @@
 
 #include <UefiUsbLibInternal.h>
 
+//  
+//  Hid RequestType Bits specifying characteristics of request.
+//  Valid values are 10100001b (0xa1) or 00100001b (0x21).
+//  The following description:
+//    7 Data transfer direction
+//        0 = Host to device
+//        1 = Device to host
+//    6..5 Type
+//        1 = Class
+//    4..0 Recipient
+//        1 = Interface
+//
 
 /**
   Get Hid Descriptor.
@@ -44,9 +57,9 @@ UsbGetHidDescriptor (
     return EFI_INVALID_PARAMETER;
   }
 
-  Request.RequestType = 0x81;
-  Request.Request     = 0x06;
-  Request.Value       = (UINT16) (0x21 << 8);
+  Request.RequestType = USB_HID_GET_DESCRIPTOR_REQ_TYPE;
+  Request.Request     = USB_REQ_GET_DESCRIPTOR;
+  Request.Value       = (UINT16) (USB_DESC_TYPE_HID << 8);
   Request.Index       = InterfaceNum;
   Request.Length      = sizeof (EFI_USB_HID_DESCRIPTOR);
 
@@ -96,9 +109,9 @@ UsbGetReportDescriptor (
   //
   // Fill Device request packet
   //
-  Request.RequestType = 0x81;
-  Request.Request     = 0x06;
-  Request.Value       = (UINT16) (0x22 << 8);
+  Request.RequestType = USB_HID_GET_DESCRIPTOR_REQ_TYPE;
+  Request.Request     = USB_REQ_GET_DESCRIPTOR;
+  Request.Value       = (UINT16) (USB_DESC_TYPE_REPORT << 8);
   Request.Index       = InterfaceNum;
   Request.Length      = DescriptorSize;
 
@@ -145,10 +158,7 @@ UsbGetProtocolRequest (
   //
   // Fill Device request packet
   //
-  Request.RequestType = 0xa1;
-  //
-  // 10100001b;
-  //
+  Request.RequestType = USB_HID_CLASS_GET_REQ_TYPE;
   Request.Request = EFI_USB_GET_PROTOCOL_REQUEST;
   Request.Value   = 0;
   Request.Index   = Interface;
@@ -199,10 +209,7 @@ UsbSetProtocolRequest (
   //
   // Fill Device request packet
   //
-  Request.RequestType = 0x21;
-  //
-  // 00100001b;
-  //
+  Request.RequestType = USB_HID_CLASS_SET_REQ_TYPE;
   Request.Request = EFI_USB_SET_PROTOCOL_REQUEST;
   Request.Value   = Protocol;
   Request.Index   = Interface;
@@ -252,10 +259,7 @@ UsbSetIdleRequest (
   //
   // Fill Device request packet
   //
-  Request.RequestType = 0x21;
-  //
-  // 00100001b;
-  //
+  Request.RequestType = USB_HID_CLASS_SET_REQ_TYPE;
   Request.Request = EFI_USB_SET_IDLE_REQUEST;
   Request.Value   = (UINT16) ((Duration << 8) | ReportId);
   Request.Index   = Interface;
@@ -305,10 +309,7 @@ UsbGetIdleRequest (
   //
   // Fill Device request packet
   //
-  Request.RequestType = 0xa1;
-  //
-  // 10100001b;
-  //
+  Request.RequestType = USB_HID_CLASS_GET_REQ_TYPE;
   Request.Request = EFI_USB_GET_IDLE_REQUEST;
   Request.Value   = ReportId;
   Request.Index   = Interface;
@@ -364,10 +365,7 @@ UsbSetReportRequest (
   //
   // Fill Device request packet
   //
-  Request.RequestType = 0x21;
-  //
-  // 00100001b;
-  //
+  Request.RequestType = USB_HID_CLASS_SET_REQ_TYPE;
   Request.Request = EFI_USB_SET_REPORT_REQUEST;
   Request.Value   = (UINT16) ((ReportType << 8) | ReportId);
   Request.Index   = Interface;
@@ -422,10 +420,7 @@ UsbGetReportRequest (
   //
   // Fill Device request packet
   //
-  Request.RequestType = 0xa1;
-  //
-  // 10100001b;
-  //
+  Request.RequestType = USB_HID_CLASS_GET_REQ_TYPE;
   Request.Request = EFI_USB_GET_REPORT_REQUEST;
   Request.Value   = (UINT16) ((ReportType << 8) | ReportId);
   Request.Index   = Interface;
diff --git a/MdePkg/Library/UefiUsbLib/UsbDxeLib.c b/MdePkg/Library/UefiUsbLib/UsbDxeLib.c
index 3e764a34a6..96466c75ef 100644
--- a/MdePkg/Library/UefiUsbLib/UsbDxeLib.c
+++ b/MdePkg/Library/UefiUsbLib/UsbDxeLib.c
@@ -1,7 +1,7 @@
 /** @file
 
-  The library provides the USB descritor, interface and protocol
-  operations.
+  The library provides the USB Standard Device Requests defined 
+  in Usb specification 9.4 section.
   
   Copyright (c) 2004 - 2007, Intel Corporation All rights
   reserved. This program and the accompanying materials are
@@ -12,7 +12,6 @@
   
   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
-  
 
 **/