Guid clsid;

    public static bool FindByProductCode(Guid productCode, ref string productName)

    public static bool FindByProductCode(Guid productCode, ref string productName)

while(0 == MsiEnumRelatedProducts("{FFFFFFFF-FFFF-FFFF-GUID-STRINGFFFFFF}", 0, iIndex++, sbProductCode)) {

public static extern uint WlanConnect(IntPtr hClientHandle,ref Guid pInterfaceGuid,ref WLAN_CONNECTION_PARAMETERS pConnectionParameters,IntPtr pReserved);

                         ByRef pInterfaceGuid As Guid, _

WlanConnect(ClientHandle,ref pInterfaceGuid,ref wlanConnectionParameters ,new IntPtr());

WlanConnect(ClientHandle, pInterfaceGuid, wlanConnectionParameters, IntPtr.Zero)

public static extern uint WlanDeleteProfile(IntPtr hClientHandle,ref Guid pInterfaceGuid,string strProfileName,IntPtr pReserved);

public static extern uint  WlanDisconnect(IntPtr hClientHandle,ref Guid pInterfaceGuid,IntPtr pReserved);

public static extern uint WlanGetAvailableNetworkList(IntPtr hClientHandle, ref Guid pInterfaceGuid, uint dwFlags, IntPtr pReserved, ref IntPtr ppAvailableNetworkList);

     Public Shared Function WlanGetAvailableNetworkList(ByVal hClientHandle As IntPtr, ByRef pInterfaceGuid As Guid, ByVal dwFlags As UInteger, ByVal pReserved As IntPtr, ByRef ppAvailableNetworkList As IntPtr) As UInteger

Guid pInterfaceGuid = ((WLAN_INTERFACE_INFO)wlanInterfaceInfoList.InterfaceInfo[0]).InterfaceGuid;

WlanGetAvailableNetworkList(ClientHandle, ref pInterfaceGuid, WLAN_AVAILABLE_NETWORK_INCLUDE_ALL_MANUAL_HIDDEN_PROFILES, new  IntPtr(), ref  ppAvailableNetworkList);

    [In, MarshalAs(UnmanagedType.LPStruct)] Guid interfaceGuid,

WlanGetProfileList(ClientHandle, pInterfaceGuid, IntPtr.Zero, out ppProfileList);

public static extern uint WlanGetProfileList(IntPtr hClientHandle,ref Guid pInterfaceGuid,IntPtr pReserved, ref IntPtr ppProfileList);

WlanGetProfileList(ClientHandle, ref pInterfaceGuid, new IntPtr(), ref ppProfileList);

        [In] ref Guid pInterfaceGuid,

    <[In]> ByRef pInterfaceGuid As Guid, ByVal OpCode As WLAN_INTF_OPCODE, _

        Guid guid;

            guid = infoList.InterfaceInfo[i].InterfaceGuid;

            if (WlanQueryInterface(handle, ref guid, WLAN_INTF_OPCODE.wlan_intf_opcode_current_connection, IntPtr.Zero, out dataSize, ref ptr, IntPtr.Zero) != 0)

     Dim guid As Guid

         guid = infoList.InterfaceInfo(i).InterfaceGuid

         If WlanQueryInterface(handle, guid, WLAN_INTF_OPCODE.wlan_intf_opcode_current_connection, IntPtr.Zero, dataSize, ptr, _

public static extern uint WlanScan(IntPtr hClientHandle,ref Guid pInterfaceGuid,IntPtr pDot11Ssid,IntPtr pIeData,IntPtr pReserved);

Public Shared Function WlanScan(ByVal hClientHandle As IntPtr, ByRef pInterfaceGuid As Guid, ByVal pDot11Ssid As IntPtr, ByVal pIeData As IntPtr, ByVal pReserved As IntPtr) As UInteger

      Guid g;

      g = infoList.InterfaceInfo[i].InterfaceGuid;

public static extern uint WlanSetInterface(IntPtr hClientHandle,ref Guid pInterfaceGuid,WLAN_INTF_OPCODE OpCode,uint dwDataSize,ref object obj ,IntPtr pReserved);

public static extern uint WlanSetProfilePosition(IntPtr hClientHandle,ref Guid pInterfaceGuid,string strProfileName,uint dwPosition,IntPtr pReserved);

public static extern uint WlanSetProfileList(IntPtr hClientHandle,ref Guid pInterfaceGuid,uint dwItems,string[] strProfileNames,IntPtr pReserved);

   [In] ref Guid iidResult, [MarshalAs(UnmanagedType.Interface)] out Object

   <[In]> ByRef iidResult As Guid, <MarshalAs(UnmanagedType.Interface), Out> ByRef _

static extern Guid CLSIDFromProgIDEx(string lpszProgID);

  Friend Shared Function CLSIDFromProgIDEx(ByVal lpszProgID As String) As Guid

static extern Guid CLSIDFromProgIDEx(string lpszProgID);

  Friend Shared Function CLSIDFromProgIDEx(ByVal lpszProgID As String) As Guid

static extern Guid CLSIDFromString(string lpsz);

static extern int CLSIDFromString(string lpsz, out Guid guid);

One of the constructors of [Guid] accepts a string.

static extern Guid CoCreateGuid();

If you like the old-style GUIDs that are generated in sequential order and contain the machine's MAC address, try UuidCreateSequential.

System.Guid.NewGuid()

   [In, MarshalAs(UnmanagedType.LPStruct)] Guid rclsid,

Guid CLSID_ShellDesktop = new Guid("00021400-0000-0000-C000-000000000046");

Guid CLSID_ShellDesktop = new Guid("00021400-0000-0000-C000-000000000046");

   [In, MarshalAs(UnmanagedType.LPStruct)] Guid rclsid,

Guid CLSID_ShellDesktop = new Guid("00021400-0000-0000-C000-000000000046");

Type shellDesktopType = Type.GetTypeFromCLSID(CLSID_ShellDesktop, true); // (Guid, serverName, throwOnError)

static extern object CoGetCallContext([In, MarshalAs(UnmanagedType.LPStruct)] Guid riid);

   [In, MarshalAs(UnmanagedType.LPStruct)] Guid riid);

[GuidAttribute("00000029-0000-0000-C000-000000000046")]

   [In, MarshalAs(UnmanagedType.LPStruct)] Guid rclsid,

   [In, MarshalAs(UnmanagedType.LPStruct)] Guid riid);

    (<[In](), MarshalAs(UnmanagedType.LPStruct)> ByVal rclsid As Guid, _

    <[In](), MarshalAs(UnmanagedType.LPStruct)> ByVal riid As Guid) _

static extern int CoGetInstanceFromFile(IntPtr pServerInfo, [In] ref Guid

   Guid riid, [MarshalAs(UnmanagedType.IUnknown)] out object ppv);

   [In, MarshalAs(UnmanagedType.LPStruct)] Guid riid);

static extern int CoMarshalInterface(UCOMIStream pStm, [In] ref Guid riid,

static extern int CoMarshalInterThreadInterfaceInStream([In] ref Guid riid,

    [MarshalAs(UnmanagedType.LPStruct)] Guid rclsid,

static extern int CoUnmarshalInterface(UCOMIStream pStm, [In] ref Guid riid,

static extern int CoUnmarshalInterface(System.Runtime.InteropServices.ComTypes.IStream pStm, [In] ref Guid riid,

static extern int CreateClassMoniker([In] ref Guid rclsid,

static extern IMoniker CreateClassMoniker([In, MarshalAs(UnmanagedType.LPStruct)]Guid guid);

The ref modifier or the [MarshalAs(LPStruct)] attribute are required on the guid parameter; otherwise it is marshaled incorrectly and the call will fail with an access violation.

    public bool PersistLoadComObject(object objComCtrl, string strGUID, byte[] buffer)

        Guid    IID_IPersistStreamInit = new Guid("7FD52380-4E07-101B-AE2D-08002B2EC713");

            if (CheckGUIDS(pPersistStream, strGUID))

     public bool CheckGUIDS(IPersistStreamInit pPersistStream, string strCtrlGUID)

          Guid ptrClsId = new Guid();

          string strStreamGUID = ptrClsId.ToString().ToUpper();

          if (strStreamGUID != strCtrlGUID.ToUpper())

          _strErrorMsg = strStreamGUID + " " + strCtrlGUID + " mismatch";

static extern int FmtIdToPropStgName([In] ref Guid pfmtid,

    <[In]()> ByRef FMTID As Guid, _

   out Guid lpiid);

static extern Guid IIDFromString(string lpsz);

    static extern int IIDFromString(string lpsz, out Guid lpiid);

       Guid   g;

    static extern Guid IIDFromString(string lpsz);

       Guid   g = IIDFromString(iid);

[System.Guid] - overloaded constructor that takes a string.

    int cPages, [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 6)] Guid[] lpPageClsID,

        Guid[] guidarray = cauuid.ToGuidArray();

        int nelements = guidarray.Length;

            o, nelements, guidarray, 0, 0, 0);

        [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 6)] Guid[] lpPageClsID,

    UInt32 cPages, [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 6)] Guid[] lpPageClsID,

   [In] ref Guid riid,

        Guid IID_IUnknown = new Guid("00000000-0000-0000-C000-000000000046");

   [In] ref Guid riid,

        Guid IID_IUnknown = new Guid("00000000-0000-0000-C000-000000000046");

static extern int OleRegGetUserType([In] ref Guid clsid, uint dwFormOfType,

  static extern int OleRegGetUserType([In] ref Guid clsid, uint dwFormOfType, out IntPtr pszBuff);

    Guid clsid = new Guid(0x3e6b91f5, 0xbc86, 0x40b8, 0x80, 0xc9, 0x41, 0xb3, 0x4b, 0x4e, 0x8f, 0x11);

static extern int ProgIDFromCLSID([In] ref Guid clsid,

static extern string ProgIDFromCLSID([In()]ref Guid clsid);

    static extern int ProgIDFromCLSID([In()]ref Guid clsid, [MarshalAs(UnmanagedType.LPWStr)]out string lplpszProgID);

       Guid   g = new Guid("88D969C0-F192-11D4-A65F-0040963251E5"); // MSXML 4.0 DOM.

    static extern string ProgIDFromCLSID([In()]ref Guid clsid);

       Guid   g = new Guid("88D969C0-F192-11D4-A65F-0040963251E5"); // MSXML 4.0 DOM.

    <Out()> ByRef FMTID As Guid) As Integer

    'A new Guid requires an array of exactly 16 bytes

    Dim fmtId As New Guid(idBytes)

Guids generated with this will return the name using the FmtIdToPropStgName Function, and can be used to generate a new IPropertyStorage interface with IPropertySetStorage.Create(). The name returned will be filled to 26 chars with the letter 'a' due to the fixed size of a Guid and the fact that we're passing all zeros in the BitArray after the name finishes to reach this size.

static extern Guid ReadClassStg(IStorage pStg);

static extern Guid ReadClassStm(UCOMIStream pStm);

   pStgOptions, IntPtr reserved2, [In] ref Guid riid,

   pStgOptions, IntPtr reserved2, [In] ref Guid riid,

   pStgOptions, IntPtr reserved2, [In] ref Guid riid,

static extern string StringFromCLSID([MarshalAs(UnmanagedType.LPStruct)] Guid rclsid);

Guid.ToString("B")

static extern int StringFromGUID2(

   [MarshalAs(UnmanagedType.LPStruct)] Guid rguid,

Guid.ToString("B")

static extern string StringFromIID([MarshalAs(kklkjlkjm.LPStruct)] Guid refiid);

Guid.ToString("B")

    [In, MarshalAs(UnmanagedType.LPStruct)] Guid rclsid);

    [In, MarshalAs(UnmanagedType.LPStruct)] Guid rclsid);

    var guids = new Guid[categoryCount];

        guids[i] = (Guid)Marshal.PtrToStructure((IntPtr)elemOffs, typeof(Guid));

        elemOffs += Marshal.SizeOf(typeof(Guid));

         heartbeatThread.Name = "Heartbeat_$" + Guid.NewGuid ().ToString ().Replace ('-', '_');

    public string szHwProfileGuid;

        string lText=lProfile.szHwProfileGuid.ToString();

        SE_WMIGUID_OBJECT,

    // http://pluralsight.com/wiki/default.aspx/Keith.GuideBook/HowToImpersonateAUserGivenHerToken.html,

    // http://pluralsight.com/wiki/default.aspx/Keith.GuideBook/HowToCreateAWindowsPrincipalGivenAToken.html,

[DllImport("advapi32", EntryPoint = "RegisterTraceGuidsW", CharSet = CharSet.Unicode, ExactSpelling = true)]

static extern unsafe uint RegisterTraceGuids([In] EtwProc cbFunc, [In] void* context, [In] ref Guid controlGuid, [In] uint guidCount, ref TraceGuidRegistration guidReg, [In] string mofImagePath, [In] string mofResourceName, out ulong regHandle);

TraceGuidRegistration (http://windowssdk.msdn.microsoft.com/library/default.asp?url=/library/en-us/etw/etw/trace_guid_registration.asp)

    internal struct TraceGuidRegistration

        internal unsafe System.Guid* Guid;