diff --git a/lib/Makefile.am b/lib/Makefile.am
index 961a1436bf..2179521da7 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -4,12 +4,12 @@
 include $(top_srcdir)/Makefile.incl
 
 #if HAVE_NSL
-nslprogs=boinc_cmd
+nslprogs=boinc_cmd$(EXEEXT)
 #endif
 
-bin_PROGRAMS = crypt_prog $(nslprogs)
+bin_PROGRAMS = crypt_prog$(EXEEXT) $(nslprogs)
 
-EXTRA_PROGRAMS = md5_test shmem_test msg_test
+EXTRA_PROGRAMS = md5_test$(EXEEXT) shmem_test$(EXEEXT) msg_test$(EXEEXT)
 
 all-local: client-bin
 
@@ -22,7 +22,7 @@ boinc_cmd_SOURCES = \
 boinc_cmd_LDADD = $(lib_LIBRARIES) $(PTHREAD_LIBS)
 
 # make a hard link to the client name.
-@CLIENT_CMD_BIN_FILENAME@: boinc_cmd
+@CLIENT_CMD_BIN_FILENAME@: boinc_cmd$(EXEEXT)
 	rm -f $@
 	rm -f $@.unmodified
 	cp $? $@.unmodified
diff --git a/lib/boinc_cmd.C b/lib/boinc_cmd.C
index 6e62f8cd4a..c358c9bfcc 100644
--- a/lib/boinc_cmd.C
+++ b/lib/boinc_cmd.C
@@ -147,7 +147,7 @@ int main(int argc, char** argv) {
 	strcpy(passwd_buf, "");
 	read_password_from_file(passwd_buf);
 
-#ifdef _WIN32
+#if defined(_WIN32) && defined(USE_WINSOCK)
     WSADATA wsdata;
     retval = WSAStartup( MAKEWORD( 1, 1 ), &wsdata);
     if (retval) {
@@ -429,7 +429,7 @@ int main(int argc, char** argv) {
         show_error(retval);
     }
 
-#ifdef _WIN32
+#if defined(_WIN32) && defined(USE_WINSOCK)
     WSACleanup();
 #endif
     return 0;
diff --git a/lib/boinc_win.h b/lib/boinc_win.h
index 2e58b808cb..cd556b3127 100644
--- a/lib/boinc_win.h
+++ b/lib/boinc_win.h
@@ -24,6 +24,11 @@
 #ifndef _BOINC_WIN_
 #define _BOINC_WIN_
 
+// Under CYGWIN we need to include config.h first.
+#ifdef __CYGWIN32__
+#include "config.h"
+#endif
+
 // Windows System Libraries
 //
 
@@ -58,26 +63,52 @@
 #define WIN32_EXTRA_LEAN      // Trims even farther.
 
 #include <windows.h>
+
+#if !defined(__CYGWIN32__) || defined(USE_WINSOCK)
+/* If we're not running under CYGWIN use windows networking */
+#undef USE_WINSOCK
+#define USE_WINSOCK 1
 #include <winsock.h>
 #include <wininet.h>
+
+#else 
+/* Under cygwin, curl was probably compiled to use <sys/socket.h> */
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <arpa/inet.h>
+#include <netdb.h>
+#define _WINSOCK_H
+#define _WINSOCKAPI_
+#define _WINSOCK2_H
+#define _WININET_H
+#define _WININETAPI_
+#endif
+
 #include <process.h>
-#ifdef __MINGW32__
+#if defined(__MINGW32__) || defined(__CYGWIN32__)
 #include <pbt.h>
 #endif
 
 #include <commctrl.h>
 #include <raserror.h>
 #include <mmsystem.h>
+#if !defined(__CYGWIN32__)
 #include <direct.h>
+#endif
 #include <io.h>
-#ifndef __MINGW32__
+#if !defined(__MINGW32__) && !defined(__CYGWIN32__)
 #include <crtdbg.h>
 #endif
+#if !defined(__CYGWIN32__)
 #include <tchar.h>
-#ifndef __MINGW32__
+#endif
+#if !defined(__MINGW32__) && !defined(__CYGWIN32__)
 #include <crtdbg.h>
 #endif
-#ifndef __MINGW32__
+#if !defined(__MINGW32__) && !defined(__CYGWIN32__)
 #include <delayimp.h>
 #endif
 // All projects should be using std::min and std::max instead of the Windows
@@ -136,9 +167,11 @@
 #include <set>
 #endif
 
-
+#ifndef __CYGWIN32__
 #define vsnprintf               _vsnprintf
 #define snprintf                _snprintf
+#define stprintf                _stprintf
+#define stricmp                 _stricmp
 #define fdopen                  _fdopen
 #define dup                     _dup
 #define unlink                  _unlink
@@ -147,7 +180,7 @@
 #define stat                    _stat
 #define finite                  _finite
 #define chdir                   _chdir
-
+#endif
 
 // On the Win32 platform include file and line number information for each
 //   memory allocation/deallocation
diff --git a/lib/diagnostics.C b/lib/diagnostics.C
index e313214fe4..2d440ebcc9 100644
--- a/lib/diagnostics.C
+++ b/lib/diagnostics.C
@@ -36,7 +36,7 @@
 #include "config.h"
 #endif
 
-#if defined(_WIN32) && !defined(__MINGW32__)
+#if defined(_WIN32) && !defined(__MINGW32__) && !defined(__CYGWIN32__)
 #include "stackwalker_win.h"
 #endif
 
@@ -392,7 +392,7 @@ LONG CALLBACK boinc_catch_signal(EXCEPTION_POINTERS *pExPtrs) {
     }
     fflush( stderr );
 
-#ifndef __MINGW32__
+#if !defined(__MINGW32__) && !defined(__CYGWIN32__)
     // Unwind the stack and spew it to stderr
     if (flags & BOINC_DIAG_DUMPCALLSTACKENABLED )
         StackwalkFilter( pExPtrs, EXCEPTION_EXECUTE_HANDLER, NULL );
@@ -469,7 +469,7 @@ void boinc_trace(const char *pszFormat, ...) {
         va_list ptr;
         va_start(ptr, pszFormat);
 
-        _vsnprintf(szBuffer, sizeof(szBuffer), pszFormat, ptr);
+        vsnprintf(szBuffer, sizeof(szBuffer), pszFormat, ptr);
 
         va_end(ptr);
 
@@ -489,7 +489,7 @@ void boinc_info_debug(const char *pszFormat, ...){
     va_list ptr;
     va_start(ptr, pszFormat);
 
-    _vsnprintf(szBuffer, sizeof(szBuffer), pszFormat, ptr);
+    vsnprintf(szBuffer, sizeof(szBuffer), pszFormat, ptr);
 
     va_end(ptr);
 
@@ -511,7 +511,7 @@ void boinc_info_release(const char *pszFormat, ...){
     va_list ptr;
     va_start(ptr, pszFormat);
 
-    _vsnprintf(szBuffer, sizeof(szBuffer), pszFormat, ptr);
+    vsnprintf(szBuffer, sizeof(szBuffer), pszFormat, ptr);
 
     va_end(ptr);
 
diff --git a/lib/diagnostics.h b/lib/diagnostics.h
index 1e3ff6fa90..9bfcfcaebb 100644
--- a/lib/diagnostics.h
+++ b/lib/diagnostics.h
@@ -129,7 +129,7 @@ extern void boinc_info_release(const char *pszFormat, ...);
 
 #else  // _DEBUG
 
-#ifdef __MINGW32__
+#if defined(__MINGW32__) || defined(__CYGWIN32__)
 #define BOINCASSERT(expr)   
 #define BOINCTRACE(...)
 #define BOINCINFO           boinc_info_release
diff --git a/lib/filesys.C b/lib/filesys.C
index 6b908443dd..44f4db0fa5 100755
--- a/lib/filesys.C
+++ b/lib/filesys.C
@@ -21,7 +21,7 @@
 #include "boinc_win.h"
 #endif
 
-#ifndef _WIN32
+#if !defined(_WIN32) || defined(__CYGWIN32__)
 #include "config.h"
 #include <cstdio>
 #include <fcntl.h>
@@ -100,8 +100,7 @@ DIRREF dir_open(const char* p) {
 #ifdef HAVE_DIRENT_H
     dirp = opendir(p);
     if (!dirp) return NULL;
-#endif
-#ifdef _WIN32
+#elif defined(_WIN32)
     if (!is_dir(p)) return NULL;
     dirp = (DIR_DESC*) calloc(sizeof(DIR_DESC), 1);
     dirp->first = true;
@@ -127,8 +126,7 @@ int dir_scan(char* p, DIRREF dirp, int p_len) {
             return ERR_READDIR;
         }
     }
-#endif
-#ifdef _WIN32
+#elif defined(_WIN32)
     WIN32_FIND_DATA data;
     while (1) {
         if (dirp->first) {
@@ -167,8 +165,7 @@ void dir_close(DIRREF dirp) {
     if (dirp) {
         closedir(dirp);
     }
-#endif
-#ifdef _WIN32
+#elif defined(_WIN32)
     if (dirp->handle != INVALID_HANDLE_VALUE) {
         FindClose(dirp->handle);
         dirp->handle = INVALID_HANDLE_VALUE;
@@ -180,9 +177,7 @@ void dir_close(DIRREF dirp) {
 DirScanner::DirScanner(string const& path) {
 #ifdef HAVE_DIRENT_H
     dirp = opendir(path.c_str());
-#endif
-
-#ifdef _WIN32
+#elif defined(_WIN32)
     first = true;
     handle = INVALID_HANDLE_VALUE;
     if (!is_dir((char*)path.c_str())) {
@@ -208,8 +203,7 @@ bool DirScanner::scan(string& s) {
             return false;
         }
     }
-#endif
-#ifdef _WIN32
+#elif defined(_WIN32)
     WIN32_FIND_DATA data;
     while (1) {
         if (first) {
@@ -243,8 +237,7 @@ DirScanner::~DirScanner() {
     if (dirp) {
         closedir(dirp);
     }
-#endif
-#ifdef _WIN32
+#elif defined(_WIN32)
     if (handle != INVALID_HANDLE_VALUE) {
         FindClose(handle);
     }
@@ -488,7 +481,7 @@ int boinc_make_dirs(const char* dirpath, const char* filepath) {
 
 int FILE_LOCK::lock(const char* filename) {
     int retval=0;
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__CYGWIN32__)
     handle = CreateFile(
         filename, GENERIC_WRITE,
         0, 0, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0
@@ -513,7 +506,7 @@ int FILE_LOCK::lock(const char* filename) {
 }
 
 int FILE_LOCK::unlock(const char* filename) {
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__CYGWIN32__)
     if (!CloseHandle(handle)) {
         perror("FILE_LOCK::unlock(): close failed.");
     }
@@ -529,7 +522,7 @@ int FILE_LOCK::unlock(const char* filename) {
 }
 
 void relative_to_absolute(const char* relname, char* path) {
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__CYGWIN32__)
     _getcwd(path, 256);
 #else
     getcwd(path, 256);
diff --git a/lib/filesys.h b/lib/filesys.h
index 48a89d5d38..93cc0a86b2 100755
--- a/lib/filesys.h
+++ b/lib/filesys.h
@@ -31,7 +31,7 @@
 #endif /* defined(_MSC_VER) && (_MSC_VER > 1020) */
 #endif /* (!defined __cplusplus) && (!defined bool) */
 
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__CYGWIN32__)
 
 typedef struct _DIR_DESC {
     char path[256];
@@ -97,7 +97,7 @@ extern void dir_close(DIRREF);
 
 
 class DirScanner {
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__CYGWIN32__)
     std::string dir;
     bool first;
     void* handle;
@@ -111,7 +111,7 @@ public:
 };
 
 struct FILE_LOCK {
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__CYGWIN32__)
     HANDLE handle;
 #else
     int fd;
diff --git a/lib/gui_rpc_client.C b/lib/gui_rpc_client.C
index 4944e72126..fe1d179bfd 100644
--- a/lib/gui_rpc_client.C
+++ b/lib/gui_rpc_client.C
@@ -20,7 +20,7 @@
 // This file is the underlying mechanism of GUI RPC client
 // (not the actual RPCs)
 
-#if defined(_WIN32) && !defined(__STDWX_H__) && !defined(_BOINC_WIN_) && !defined(_AFX_STDAFX_H_)
+#if defined(_WIN32) && !defined(__STDWX_H__) && !defined(_BOINC_WIN_) && !defined(_AFX_STDAFX_H_) 
 #include "boinc_win.h"
 #endif
 
@@ -79,7 +79,7 @@ void RPC_CLIENT::close() {
 int RPC_CLIENT::init(const char* host, int port) {
     double client_time = 0.0;
     int retval;
-	memset(&addr, 0, sizeof(addr));
+    memset(&addr, 0, sizeof(addr));
     addr.sin_family = AF_INET;
     if (port) {
         addr.sin_port = htons(port);
diff --git a/lib/gui_rpc_client.h b/lib/gui_rpc_client.h
index ee97317f5b..258e4b9dd9 100644
--- a/lib/gui_rpc_client.h
+++ b/lib/gui_rpc_client.h
@@ -19,7 +19,7 @@
 
 // a C++ interface to BOINC GUI RPC
 
-#ifndef _WIN32
+#if !defined(_WIN32) || defined (__CYGWIN__)
 #include <stdio.h>
 #include <string>
 #include <vector>
diff --git a/lib/network.C b/lib/network.C
index 53d8203c5c..a42a605057 100644
--- a/lib/network.C
+++ b/lib/network.C
@@ -31,6 +31,7 @@
 #include <arpa/inet.h>
 #include <netdb.h>
 #include <fcntl.h>
+#include <errno.h>
 #endif
 
 #include "error_numbers.h"
@@ -38,7 +39,7 @@
 
 const char* socket_error_str() {
     static char buf[80];
-#ifdef _WIN32
+#if defined(_WIN32) && defined(USE_WINSOCK)
     int e = WSAGetLastError();
     switch (e) {
     case WSANOTINITIALISED:
@@ -74,6 +75,11 @@ const char* socket_error_str() {
         return "a nonrecoverable error occurred";
     case TRY_AGAIN:
         return "host not found or server failure";
+#ifdef NETDB_INTERNAL
+    case NETDB_INTERNAL:
+		sprintf(buf,"network internal error %d",errno);
+		return buf;
+#endif
     }
     sprintf(buf, "error %d", h_errno);
     return buf;
@@ -113,7 +119,7 @@ int boinc_socket(int& fd) {
 
 int boinc_socket_asynch(int fd, bool asynch) {
     if (asynch) {
-#ifdef WIN32
+#if defined(_WIN32) && defined(USE_WINSOCK)
         unsigned long one = 1;
         ioctlsocket(fd, FIONBIO, &one);
 #else
@@ -127,7 +133,7 @@ int boinc_socket_asynch(int fd, bool asynch) {
         }
 #endif
     } else {
-#ifdef WIN32
+#if defined(_WIN32) && defined(USE_WINSOCK)
         unsigned long zero = 0;
         ioctlsocket(fd, FIONBIO, &zero);
 #else
@@ -145,7 +151,7 @@ int boinc_socket_asynch(int fd, bool asynch) {
 }
 
 void boinc_close_socket(int sock) {
-#ifdef _WIN32
+#if defined(_WIN32) && defined(USE_WINSOCK)
     closesocket(sock);
 #else
     close(sock);
@@ -155,7 +161,7 @@ void boinc_close_socket(int sock) {
 int get_socket_error(int fd) {
     boinc_socklen_t intsize = sizeof(int);
     int n;
-#ifdef WIN32
+#if defined(_WIN32) && defined(USE_WINSOCK)
     getsockopt(fd, SOL_SOCKET, SO_ERROR, (char *)&n, &intsize);
 #elif defined(__APPLE__)
     getsockopt(fd, SOL_SOCKET, SO_ERROR, &n, (int *)&intsize);
@@ -170,7 +176,7 @@ int get_socket_error(int fd) {
     return n;
 }
 
-#ifdef _WIN32
+#if defined(_WIN32) && defined(USE_WINSOCK)
 
 typedef BOOL (WINAPI *GetStateProc)( OUT LPDWORD lpdwFlags, IN DWORD dwReserved);
 
diff --git a/lib/network.h b/lib/network.h
index 3a82f97f79..6a66626bd1 100644
--- a/lib/network.h
+++ b/lib/network.h
@@ -24,6 +24,8 @@
 #ifndef _WIN32
 #include <unistd.h>
 #include "config.h"
+#else
+#include "boinc_win.h"
 #endif
 
 struct FDSET_GROUP {
@@ -47,7 +49,7 @@ extern void boinc_close_socket(int sock);
 extern int get_socket_error(int fd);
 extern const char* socket_error_str();
 
-#if defined(_WIN32)
+#if defined(_WIN32) && defined(USE_WINSOCK)
 typedef int boinc_socklen_t;
 #define SHUT_WR SD_SEND
 #elif defined( __APPLE__)
@@ -62,7 +64,7 @@ typedef BOINC_SOCKLEN_T boinc_socklen_t;
 
 extern int get_connected_state();
 
-#ifdef _WIN32
+#if defined(_WIN32) && defined(USE_WINSOCK)
 extern int WinsockInitialize();
 extern int WinsockCleanup();
 #endif
diff --git a/lib/parse.h b/lib/parse.h
index db431df7df..9acd88fe74 100644
--- a/lib/parse.h
+++ b/lib/parse.h
@@ -24,6 +24,8 @@
 #include <cstdio>
 #include <cstdlib>
 #include <string>
+#else
+#include "boinc_win.h"
 #endif
 
 extern bool parse(char* , char* );
diff --git a/lib/util.C b/lib/util.C
index a6a2d348af..bf7096100f 100755
--- a/lib/util.C
+++ b/lib/util.C
@@ -21,7 +21,7 @@
 #include "boinc_win.h"
 #endif
 
-#ifdef _WIN32
+#ifndef M_LN2
 #define M_LN2      0.693147180559945309417
 #endif