diff --git a/icu4c/source/common/Makefile.in b/icu4c/source/common/Makefile.in
index 96b67b93873..dc8ff7bfa72 100644
--- a/icu4c/source/common/Makefile.in
+++ b/icu4c/source/common/Makefile.in
@@ -47,7 +47,7 @@ DYNAMICCXXFLAGS = $(SHAREDLIBCXXFLAGS)
 
 # Data packaging options are set at configure time with --with-data-packaging.
 CPPFLAGS += -I. -I$(srcdir) $(LIBCPPFLAGS) @DATA_PACKAGING_CPPFLAGS@
-DEFS += -DU_LIBICUDATA_NAME=\"$(ICUDATA_NAME)\"
+DEFS += -DU_LIBICUDATA_NAME=\"$(ICUDATA_NAME)\" -DU_COMMON_IMPLEMENTATION
 
 # $(LIBICUDT) is either stub data or the real DLL common data.
 LIBS = $(LIBICUDT) $(DEFAULT_LIBS)
diff --git a/icu4c/source/common/unicode/platform.h.in b/icu4c/source/common/unicode/platform.h.in
index c73d967849a..69a5b4dd249 100644
--- a/icu4c/source/common/unicode/platform.h.in
+++ b/icu4c/source/common/unicode/platform.h.in
@@ -232,13 +232,12 @@ typedef unsigned short uint16_t;
 #define U_EXPORT
 /* U_CALLCONV is releated to U_EXPORT2 */
 #define U_EXPORT2
-#define U_IMPORT 
 
 /* cygwin needs to export/import data */
 #ifdef U_CYGWIN
-#define U_DATA_IMPORT __declspec(dllimport)
+#define U_IMPORT __declspec(dllimport)
 #else
-#define U_DATA_IMPORT 
+#define U_IMPORT 
 #endif
 
 /*===========================================================================*/
diff --git a/icu4c/source/common/unicode/pwin32.h b/icu4c/source/common/unicode/pwin32.h
index 55b2c85979e..1b39246b0be 100644
--- a/icu4c/source/common/unicode/pwin32.h
+++ b/icu4c/source/common/unicode/pwin32.h
@@ -144,7 +144,6 @@ typedef unsigned short uint16_t;
 #define U_EXPORT __declspec(dllexport)
 #define U_EXPORT2
 #define U_IMPORT __declspec(dllimport)
-#define U_DATA_IMPORT __declspec(dllimport)
 
 /*===========================================================================*/
 /* Code alignment and C function inlining                                    */
diff --git a/icu4c/source/common/unicode/utf8.h b/icu4c/source/common/unicode/utf8.h
index f467de7a25a..a5b58618126 100644
--- a/icu4c/source/common/unicode/utf8.h
+++ b/icu4c/source/common/unicode/utf8.h
@@ -43,7 +43,7 @@
 U_CAPI const uint8_t 
 utf8_countTrailBytes[256];
 #else
-U_CFUNC U_DATA_IMPORT const uint8_t /* U_IMPORT2? */ /*U_IMPORT*/ 
+U_CFUNC U_IMPORT const uint8_t /* U_IMPORT2? */ /*U_IMPORT*/ 
 utf8_countTrailBytes[256];
 #endif
 
diff --git a/icu4c/source/extra/ustdio/Makefile.in b/icu4c/source/extra/ustdio/Makefile.in
index 9861fbc6c2d..e46039f29c8 100644
--- a/icu4c/source/extra/ustdio/Makefile.in
+++ b/icu4c/source/extra/ustdio/Makefile.in
@@ -40,6 +40,7 @@ DYNAMICCFLAGS = $(SHAREDLIBCFLAGS)
 DYNAMICCXXFLAGS = $(SHAREDLIBCXXFLAGS)
 
 CPPFLAGS += -I$(top_builddir)/common -I$(top_srcdir)/common -I$(top_srcdir)/i18n $(LIBCPPFLAGS)
+DEFS += -DU_USTDIO_IMPLEMENTATION
 LIBS = $(LIBICUUC) $(LIBICUI18N) $(DEFAULT_LIBS)
 
 OBJECTS = locbund.o loccache.o ufile.o ufmt_cmn.o uprintf.o uprntf_p.o \
diff --git a/icu4c/source/i18n/Makefile.in b/icu4c/source/i18n/Makefile.in
index 3aaedc03d2b..3e20bd6f18a 100644
--- a/icu4c/source/i18n/Makefile.in
+++ b/icu4c/source/i18n/Makefile.in
@@ -40,6 +40,7 @@ DYNAMICCFLAGS = $(SHAREDLIBCFLAGS)
 DYNAMICCXXFLAGS = $(SHAREDLIBCXXFLAGS)
 
 CPPFLAGS += -I$(srcdir) -I$(top_builddir)/common -I$(top_srcdir)/common $(LIBCPPFLAGS)
+DEFS += -DU_I18N_IMPLEMENTATION
 LIBS = $(LIBICUUC) $(DEFAULT_LIBS)
 
 OBJECTS = ucln_in.o \
diff --git a/icu4c/source/layout/Makefile.in b/icu4c/source/layout/Makefile.in
index f608773c873..73d7bcbf7c8 100644
--- a/icu4c/source/layout/Makefile.in
+++ b/icu4c/source/layout/Makefile.in
@@ -37,6 +37,7 @@ DYNAMICCFLAGS = $(SHAREDLIBCFLAGS)
 DYNAMICCXXFLAGS = $(SHAREDLIBCXXFLAGS)
 
 CPPFLAGS += -I$(srcdir) -I$(top_builddir)/common -I$(srcdir)/unicode -I$(srcdir)/.. -I$(top_builddir)/common -I$(top_srcdir)/common $(LIBCPPFLAGS)
+DEFS += -DU_LAYOUT_IMPLEMENTATION
 LIBS = $(DEFAULT_LIBS)
 
 
diff --git a/icu4c/source/test/intltest/tsmthred.cpp b/icu4c/source/test/intltest/tsmthred.cpp
index 61bdb3c9685..4d130032e0b 100644
--- a/icu4c/source/test/intltest/tsmthred.cpp
+++ b/icu4c/source/test/intltest/tsmthred.cpp
@@ -12,6 +12,12 @@
 
 #include <unicode/umachine.h>
 
+// Just turn off threads on cygwin, so that we can test
+// the other stuff. This needs to be investigated further.
+#if defined(U_CYGWIN)
+#define ICU_USE_THREADS 0
+#endif
+
 #if !defined(WIN32) && !defined(XP_MAC) && !defined(U_RHAPSODY)
 #define POSIX 1
 #endif
diff --git a/icu4c/source/tools/ctestfw/ctest.c b/icu4c/source/tools/ctestfw/ctest.c
index 17e23f2a70b..4fafaa4488d 100644
--- a/icu4c/source/tools/ctestfw/ctest.c
+++ b/icu4c/source/tools/ctestfw/ctest.c
@@ -34,6 +34,10 @@ static const struct TestNode* currentTest;
 typedef enum { RUNTESTS, SHOWTESTS } TestMode;
 #define TEST_SEPARATOR '/'
 
+#ifndef C_TEST_IMPL
+#define C_TEST_IMPL
+#endif
+
 #include "unicode/ctest.h"
 
 static char ERROR_LOG[MAX_TEST_LOG][MAXTESTNAME];
diff --git a/icu4c/source/tools/ctestfw/unicode/ctest.h b/icu4c/source/tools/ctestfw/unicode/ctest.h
index 5267b22b2ab..440c473f4de 100644
--- a/icu4c/source/tools/ctestfw/unicode/ctest.h
+++ b/icu4c/source/tools/ctestfw/unicode/ctest.h
@@ -11,9 +11,10 @@
 #ifndef CTEST_H
 #define CTEST_H
 
+#include "unicode/utypes.h"
 
 /*Deals with imports and exports of the dynamic library*/
-#ifdef _WIN32
+#if defined(_WIN32) || defined(U_CYGWIN)
     #define T_CTEST_EXPORT __declspec(dllexport)
     #define T_CTEST_IMPORT __declspec(dllimport)
 #else