diff --git a/eng/pipelines/common/platform-matrix.yml b/eng/pipelines/common/platform-matrix.yml
index b0753c0c69ef23..42e3df05d637de 100644
--- a/eng/pipelines/common/platform-matrix.yml
+++ b/eng/pipelines/common/platform-matrix.yml
@@ -169,7 +169,7 @@ jobs:
       archType: wasm
       platform: WebAssembly_wasm
       container:
-        image: ubuntu-16.04-20200401182342-fe8b85d
+        image: ubuntu-18.04-webassembly-20200407092345-059fef0
         registry: mcr
       jobParameters:
         runtimeFlavor: ${{ parameters.runtimeFlavor }}
diff --git a/eng/pipelines/mono/templates/build-job.yml b/eng/pipelines/mono/templates/build-job.yml
index 9beb7e42f0028e..33f25fed2d0ba6 100644
--- a/eng/pipelines/mono/templates/build-job.yml
+++ b/eng/pipelines/mono/templates/build-job.yml
@@ -71,6 +71,13 @@ jobs:
     - ${{ if eq(parameters.osGroup, 'Android') }}:
       - name: osOverride
         value: -os Android
+    - ${{ if eq(parameters.osGroup, 'WebAssembly') }}:
+      - name: EMSDK_PATH
+        value: $(Build.BinariesDirectory)/emsdk
+      - name: archType
+        value: wasm
+      - name: osOverride
+        value: '-os WebAssembly'
     - ${{ parameters.variables }}
 
     steps:
@@ -87,6 +94,16 @@ jobs:
       - script: $(Build.SourcesDirectory)\eng\common\init-tools-native.cmd -InstallDirectory $(Build.SourcesDirectory)\native-tools -Force
         displayName: Install native dependencies
 
+    - ${{ if eq(parameters.osGroup, 'WebAssembly') }}:
+      - script: |
+          set -v
+          EMSCRIPTEN_VERSION=1.39.9
+          git clone https://github.com/emscripten-core/emsdk.git $(EMSDK_PATH)
+          cd $(EMSDK_PATH)
+          ./emsdk install ${EMSCRIPTEN_VERSION}-upstream
+          ./emsdk activate --embedded ${EMSCRIPTEN_VERSION}-upstream
+        displayName: Install Emscripten
+
     # Build
     - ${{ if ne(parameters.osGroup, 'Windows_NT') }}:
       - script: ./build$(scriptExt) -subsetcategory mono -c $(buildConfig) -arch $(archType) $(osOverride) -ci /p:MonoEnableLLVM=${{ parameters.llvm }}
diff --git a/eng/pipelines/runtime.yml b/eng/pipelines/runtime.yml
index 2bf8140c146e83..11967488ff65b6 100644
--- a/eng/pipelines/runtime.yml
+++ b/eng/pipelines/runtime.yml
@@ -264,6 +264,7 @@ jobs:
     - Linux_arm
     - Linux_arm64
     - Linux_musl_x64
+    - WebAssembly_wasm
     # - Linux_musl_arm64
     - Windows_NT_x64
     # - Windows_NT_x86
diff --git a/src/mono/Directory.Build.props b/src/mono/Directory.Build.props
index 3492d626747429..a14345797c1766 100644
--- a/src/mono/Directory.Build.props
+++ b/src/mono/Directory.Build.props
@@ -41,7 +41,8 @@
     <TargetsiOSSimulator Condition="'$(TargetsiOS)' == 'true' and '$(Platform)' == 'x64'">true</TargetsiOSSimulator>
     <TargetsAndroid Condition="'$(TargetOS)' == 'Android'">true</TargetsAndroid>
     <TargetsWindows Condition="'$(TargetOS)' == 'Windows_NT'">true</TargetsWindows>
-    <TargetsUnix Condition="'$(TargetsFreeBSD)' == 'true' or '$(TargetsLinux)' == 'true' or '$(TargetsNetBSD)' == 'true' or '$(TargetsOSX)' == 'true' or '$(TargetsiOS)' == 'true' or '$(TargetsAndroid)' == 'true'">true</TargetsUnix>
+    <TargetsWASM Condition="'$(TargetOS)' == 'WebAssembly'">true</TargetsWASM>
+    <TargetsUnix Condition="'$(TargetsFreeBSD)' == 'true' or '$(TargetsLinux)' == 'true' or '$(TargetsNetBSD)' == 'true' or '$(TargetsOSX)' == 'true' or '$(TargetsiOS)' == 'true' or '$(TargetsAndroid)' == 'true' or '$(TargetsWASM)' == 'true'">true</TargetsUnix>
   </PropertyGroup>
 
   <PropertyGroup>
diff --git a/src/mono/mono.proj b/src/mono/mono.proj
index 55c4e17fba9993..5a886bcbbd3ca9 100644
--- a/src/mono/mono.proj
+++ b/src/mono/mono.proj
@@ -18,6 +18,8 @@
     <MonoFileName Condition="'$(TargetsAndroid)' == 'true'">libmonosgen-2.0.so</MonoFileName>
     <MonoStaticFileName Condition="'$(TargetsiOS)' == 'true'">libmono.a</MonoStaticFileName>
     <MonoStaticFileName Condition="'$(TargetsAndroid)' == 'true'">libmonosgen-2.0.a</MonoStaticFileName>
+    <MonoFileName Condition="'$(TargetsWASM)' == 'true'">libmono.a</MonoFileName>
+    <MonoStaticFileName Condition="'$(TargetsWASM)' == 'true'">libmono.a</MonoStaticFileName>
     <MonoFileName Condition="'$(MonoFileName)' == ''">$(CoreClrFileName)</MonoFileName>
     <CoreClrTestConfig Condition="'$(CoreClrTestConfig)' == ''">$(Configuration)</CoreClrTestConfig>
     <LibrariesTestConfig Condition="'$(LibrariesTestConfig)' == ''">$(Configuration)</LibrariesTestConfig>
@@ -411,6 +413,31 @@
       <_MonoSTRIPOption>STRIP="$(_MonoTuple)-strip"</_MonoSTRIPOption>
     </PropertyGroup>
 
+    <Error Condition="'$(TargetsWASM)' == 'true' and '$(EMSDK_PATH)' == ''" Text="The EMSDK_PATH environment variable should be set pointing to the emscripten SDK root dir."/>
+
+    <!-- WASM specific options -->
+    <ItemGroup Condition="'$(TargetsWASM)' == 'true'">
+      <_MonoConfigureParams Include="--host=wasm32"/>
+      <_MonoConfigureParams Include="--disable-boehm" />
+      <_MonoConfigureParams Include="--disable-btls" />
+      <_MonoConfigureParams Include="--disable-executables" />
+      <_MonoConfigureParams Include="--disable-iconv" />
+      <_MonoConfigureParams Include="--disable-mcs-build" />
+      <_MonoConfigureParams Include="--disable-nls" />
+      <_MonoConfigureParams Include="--disable-visibility-hidden" />
+      <_MonoConfigureParams Include="--enable-maintainer-mode" />
+      <_MonoConfigureParams Include="--enable-llvm-runtime"/>
+      <_MonoConfigureParams Include="--enable-icall-export"/>
+      <_MonoConfigureParams Include="--disable-icall-tables"/>
+      <_MonoConfigureParams Include="--disable-crash-reporting"/>
+      <_MonoConfigureParams Include="--with-bitcode=yes"/>
+      <_MonoConfigureParams Include="--enable-minimal=ssa,com,jit,reflection_emit_save,portability,assembly_remapping,attach,verifier,full_messages,appdomains,security,sgen_marksweep_conc,sgen_split_nursery,sgen_gc_bridge,logging,remoting,shared_perfcounters,sgen_debug_helpers,soft_debug,interpreter,assert_messages,cleanup,mdb,gac"/>
+      <!-- FIXME: -Os -->
+      <_MonoCFLAGS Include="-fexceptions" />
+      <_MonoCXXFLAGS Include="-fexceptions -s DISABLE_EXCEPTION_CATCHING=0" />
+      <_MonoAC_VARS Include="ac_cv_func_shm_open_working_with_mmap=no" />
+    </ItemGroup>
+
     <!-- Linux options -->
     <ItemGroup Condition="'$(TargetsLinux)' == true">
       <_MonoCFLAGS Include="-Wl,--build-id" />
@@ -443,9 +470,10 @@
       <_MonoLDFLAGSOption Condition="@(_MonoLDFLAGS->Count()) &gt; 0">LDFLAGS="@(_MonoLDFLAGS, ' ')"</_MonoLDFLAGSOption>
       <_MonoCCLDFLAGSOption Condition="@(_MonoCCLDFLAGS->Count()) &gt; 0">CCLDFLAGS="@(_MonoCCLDFLAGS, ' ')"</_MonoCCLDFLAGSOption>
 
-      <_MonoConfigureCommand>@(_MonoConfigureParams, ' ') @(_MonoAC_VARS, ' ') $(_MonoCFLAGSOption) $(_MonoCXXFLAGSOption) $(_MonoCPPFLAGSOption) $(_MonoCXXCPPFLAGSOption) $(_MonoLDFLAGSOption) $(_MonoCCLDFLAGSOption) $(_MonoCCOption) $(_MonoCXXOption) $(_MonoAROption) $(_MonoASOption) $(_MonoCPPOption) $(_MonoCXXCPPOption) $(_MonoDLLTOOLOption) $(_MonoLDOption) $(_MonoOBJDUMPOption) $(_MonoRANLIBOption) $(_MonoCMAKEOption) $(_MonoSTRIPOption)</_MonoConfigureCommand>
-      <_MonoConfigureCommand Condition="'$(_MonoCCOption)' == '' and '$(_MonoCXXOption)' == ''">bash -c 'source $(RepositoryEngineeringDir)native/init-compiler.sh $(Platform) clang &amp;&amp; $(MonoProjectRoot)configure $(_MonoConfigureCommand)'</_MonoConfigureCommand>
-      <_MonoConfigureCommand Condition="'$(_MonoCCOption)' != '' and '$(_MonoCXXOption)' != ''">$(MonoProjectRoot)configure $(_MonoConfigureCommand)</_MonoConfigureCommand>
+      <_MonoConfigureOptions>@(_MonoConfigureParams, ' ') @(_MonoAC_VARS, ' ') $(_MonoCFLAGSOption) $(_MonoCXXFLAGSOption) $(_MonoCPPFLAGSOption) $(_MonoCXXCPPFLAGSOption) $(_MonoLDFLAGSOption) $(_MonoCCLDFLAGSOption) $(_MonoCCOption) $(_MonoCXXOption) $(_MonoAROption) $(_MonoASOption) $(_MonoCPPOption) $(_MonoCXXCPPOption) $(_MonoDLLTOOLOption) $(_MonoLDOption) $(_MonoOBJDUMPOption) $(_MonoRANLIBOption) $(_MonoCMAKEOption) $(_MonoSTRIPOption)</_MonoConfigureOptions>
+      <_MonoConfigureCommand Condition="'$(_MonoCCOption)' == '' and '$(_MonoCXXOption)' == ''">bash -c 'source $(RepositoryEngineeringDir)native/init-compiler.sh $(Platform) clang &amp;&amp; $(MonoProjectRoot)configure $(_MonoConfigureOptions)'</_MonoConfigureCommand>
+      <_MonoConfigureCommand Condition="'$(_MonoCCOption)' != '' and '$(_MonoCXXOption)' != ''">$(MonoProjectRoot)configure $(_MonoConfigureOptions)</_MonoConfigureCommand>
+      <_MonoConfigureCommand Condition="'$(TargetsWASM)' == 'true'">bash -c 'source $(EMSDK_PATH)/emsdk_env.sh &amp;&amp; emconfigure $(MonoProjectRoot)configure $(_MonoConfigureOptions)'</_MonoConfigureCommand>
     </PropertyGroup>
 
     <!-- AOT cross-compiler specific options -->
@@ -464,7 +492,7 @@
     <!-- Configure target runtime -->
     <MakeDir Directories="$(MonoObjDir)" />
     <Message Text="--- Configuring Mono with '$(_MonoConfigureCommand)' ---" Importance="High" />
-    <Exec Command="NOCONFIGURE=1 $(MonoProjectRoot)autogen.sh" />
+    <Exec Command="NOCONFIGURE=1 $(MonoProjectRoot)autogen.sh" IgnoreStandardErrorWarningFormat="true"/>
     <Exec Command="$(_MonoConfigureCommand)" WorkingDirectory="$(MonoObjDir)" IgnoreStandardErrorWarningFormat="true" />
     <Touch Files="$(MonoObjDir)config.h" />
 
@@ -478,7 +506,7 @@
     <Touch Condition="'$(_MonoAotCrossConfigureCommand)' != ''" Files="$(MonoObjDir)cross/config.h" />
   </Target>
 
-  <Target Name="BuildMonoRuntimeUnix" Condition="'$(OS)' != 'Windows_NT'" DependsOnTargets="ConfigureMonoRuntimeUnix">
+  <Target Name="BuildMonoRuntimeUnix" Condition="'$(OS)' != 'Windows_NT' and '$(TargetsWASM)' != 'true'" DependsOnTargets="ConfigureMonoRuntimeUnix">
     <Message Text="--- Building Mono ---" Importance="High" />
     <Exec Command="make -j$([System.Environment]::ProcessorCount)" IgnoreStandardErrorWarningFormat="true" WorkingDirectory="$(MonoObjDir)" />
     <Exec Condition="'$(TargetsiOS)' == 'true' or '$(TargetsAndroid)' == 'true'" Command="make install -j$([System.Environment]::ProcessorCount)" IgnoreStandardErrorWarningFormat="true" WorkingDirectory="$(MonoObjDir)" />
@@ -488,6 +516,12 @@
     <Exec Condition="'$(TargetsiOS)' == 'true' and '$(TargetsiOSSimulator)' != 'true'" Command="make install -j$([System.Environment]::ProcessorCount)" IgnoreStandardErrorWarningFormat="true" WorkingDirectory="$(MonoObjDir)cross" />
   </Target>
 
+  <Target Name="BuildMonoRuntimeWASM" Condition="'$(TargetsWASM)' == 'true'" DependsOnTargets="ConfigureMonoRuntimeUnix">
+    <Message Text="--- Building Mono (WASM) ---" Importance="High" />
+    <Exec Command="bash -c 'source $(EMSDK_PATH)/emsdk_env.sh &amp;&amp; make -j$([System.Environment]::ProcessorCount)'" IgnoreStandardErrorWarningFormat="true" WorkingDirectory="$(MonoObjDir)" />
+    <Exec Command="bash -c 'source $(EMSDK_PATH)/emsdk_env.sh &amp;&amp; make install -j$([System.Environment]::ProcessorCount)'" IgnoreStandardErrorWarningFormat="true" WorkingDirectory="$(MonoObjDir)" />
+  </Target>
+
   <!-- Windows Mono runtime build -->
   <Target Name="BuildMonoRuntimeWindows" Condition="'$(OS)' == 'Windows_NT'">
 
@@ -657,13 +691,14 @@
 
   <!-- Ordering matters! Overwriting the Build target. -->
   <!-- General targets -->
-  <Target Name="Build" DependsOnTargets="BuildMonoRuntimeUnix;BuildMonoRuntimeWindows">
+  <Target Name="Build" DependsOnTargets="BuildMonoRuntimeUnix;BuildMonoRuntimeWindows;BuildMonoRuntimeWASM">
     <PropertyGroup>
       <_MonoRuntimeFilePath Condition="'$(TargetsWindows)' == 'true' and '$(Platform)' == 'x64'">$(MonoObjDir)x64\Bin\$(Configuration)\mono-2.0-sgen.dll</_MonoRuntimeFilePath>
       <_MonoRuntimeFilePath Condition="'$(TargetsWindows)' == 'true' and '$(Platform)' == 'x86'">$(MonoObjDir)Win32\Bin\$(Configuration)\mono-2.0-sgen.dll</_MonoRuntimeFilePath>
       <_MonoRuntimeFilePath Condition="'$(TargetsOSX)' == 'true'">$(MonoObjDir)mono\mini\.libs\libmonosgen-2.0.dylib</_MonoRuntimeFilePath>
       <_MonoRuntimeFilePath Condition="'$(TargetsiOS)' == 'true'">$(MonoObjDir)out\lib\libmonosgen-2.0.dylib</_MonoRuntimeFilePath>
       <_MonoRuntimeFilePath Condition="'$(TargetsAndroid)' == 'true'">$(MonoObjDir)out\lib\libmonosgen-2.0.so</_MonoRuntimeFilePath>
+      <_MonoRuntimeFilePath Condition="'$(TargetsWASM)' == 'true'">$(MonoObjDir)mono\mini\.libs\libmonosgen-2.0.a</_MonoRuntimeFilePath>
       <_MonoRuntimeFilePath Condition="'$(_MonoRuntimeFilePath)' == ''">$(MonoObjDir)mono\mini\.libs\libmonosgen-2.0.so</_MonoRuntimeFilePath>
       <_MonoRuntimeStaticFilePath Condition="'$(TargetsiOS)' == 'true' or '$(TargetsAndroid)' == 'true'">$(MonoObjDir)out\lib\libmonosgen-2.0.a</_MonoRuntimeStaticFilePath>
       <_MonoAotCrossFilePath Condition="'$(TargetsiOS)' == 'true' and '$(Platform)' == 'arm64'">$(MonoObjDir)cross\out\bin\aarch64-darwin-mono-sgen</_MonoAotCrossFilePath>
@@ -691,7 +726,7 @@
     <Copy SourceFiles="@(_MonoIncludeArtifacts)"
           DestinationFiles="@(_MonoIncludeArtifacts->'$(BinDir)include\%(RecursiveDir)%(Filename)%(Extension)')"
           SkipUnchangedFiles="true"
-          Condition="'$(TargetsiOS)' == 'true' or '$(TargetsAndroid)' == 'true'"/>
+          Condition="'$(TargetsiOS)' == 'true' or '$(TargetsAndroid)' == 'true' or '$(TargetsWASM)' == 'true'"/>
 
     <Exec Condition="'$(TargetsOSX)' == 'true' or '$(TargetsiOS)' == 'true'" Command="install_name_tool -id @rpath/$(MonoFileName) $(BinDir)$(MonoFileName)" />
   </Target>
diff --git a/src/mono/netcore/System.Private.CoreLib/System.Private.CoreLib.csproj b/src/mono/netcore/System.Private.CoreLib/System.Private.CoreLib.csproj
index cd45f2dc12df44..8f303e8c6e746f 100644
--- a/src/mono/netcore/System.Private.CoreLib/System.Private.CoreLib.csproj
+++ b/src/mono/netcore/System.Private.CoreLib/System.Private.CoreLib.csproj
@@ -18,7 +18,7 @@
     <!-- Force System.Private.CoreLib.dll into a special IL output directory -->
     <OutputPath>$(BinDir)IL/</OutputPath>
     <Configurations>Debug;Release;Checked</Configurations>
-    <Platforms>x64;x86;arm;arm64;wasm32</Platforms>
+    <Platforms>x64;x86;arm;arm64;wasm</Platforms>
 
     <ILLinkClearInitLocals>true</ILLinkClearInitLocals>
     <ILLinkTrimAssembly>true</ILLinkTrimAssembly>
@@ -82,7 +82,7 @@
     <PlatformTarget>AnyCPU</PlatformTarget>
     <DefineConstants>TARGET_64BIT;TARGET_ARM64;$(DefineConstants)</DefineConstants>
   </PropertyGroup>
-  <PropertyGroup Condition="'$(Platform)' == 'wasm32'">
+  <PropertyGroup Condition="'$(Platform)' == 'wasm'">
     <PlatformTarget>AnyCPU</PlatformTarget>
     <DefineConstants>TARGET_32BIT;$(DefineConstants)</DefineConstants>
   </PropertyGroup>