diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -13,6 +13,7 @@ on:
     - '**/*.rst'
   pull_request:
     branches:
+    - pegen
     - master
     - 3.8
     - 3.7
@@ -50,6 +51,22 @@ jobs:
   build_macos:
     name: 'macOS'
     runs-on: macos-latest
+    env:
+      PYTHONOLDPARSER: old
+    steps:
+    - uses: actions/checkout@v1
+    - name: Configure CPython
+      run: ./configure --with-pydebug --with-openssl=/usr/local/opt/openssl --prefix=/opt/python-dev
+    - name: Build CPython
+      run: make -j4
+    - name: Display build info
+      run: make pythoninfo
+    - name: Tests
+      run: make buildbottest TESTOPTS="-j4 -uall,-cpu"
+
+  build_macos_pegen:
+    name: 'macOS - Pegen'
+    runs-on: macos-latest
     steps:
     - uses: actions/checkout@v1
     - name: Configure CPython
@@ -64,6 +81,34 @@ jobs:
   build_ubuntu:
     name: 'Ubuntu'
     runs-on: ubuntu-latest
+    env:
+      OPENSSL_VER: 1.1.1f
+      PYTHONOLDPARSER: old
+    steps:
+    - uses: actions/checkout@v1
+    - name: Install Dependencies
+      run: sudo ./.github/workflows/posix-deps-apt.sh
+    - name: 'Restore OpenSSL build'
+      id: cache-openssl
+      uses: actions/cache@v1
+      with:
+        path: ./multissl/openssl/${{ env.OPENSSL_VER }}
+        key: ${{ runner.os }}-multissl-openssl-${{ env.OPENSSL_VER }}
+    - name: Install OpenSSL
+      if: steps.cache-openssl.outputs.cache-hit != 'true'
+      run: python3 Tools/ssl/multissltests.py --steps=library --base-directory $PWD/multissl --openssl $OPENSSL_VER --system Linux
+    - name: Configure CPython
+      run: ./configure --with-pydebug --with-openssl=$PWD/multissl/openssl/$OPENSSL_VER
+    - name: Build CPython
+      run: make -j4
+    - name: Display build info
+      run: make pythoninfo
+    - name: Tests
+      run: xvfb-run make buildbottest TESTOPTS="-j4 -uall,-cpu"
+
+  build_ubuntu_pegen:
+    name: 'Ubuntu - Pegen'
+    runs-on: ubuntu-latest
     env:
       OPENSSL_VER: 1.1.1f
     steps:
diff --git a/.travis.yml b/.travis.yml
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,5 +1,5 @@
 language: c
-dist: xenial
+dist: bionic
 
 # To cache doc-building dependencies and C compiler output.
 cache:
@@ -22,6 +22,7 @@ env:
 branches:
   only:
     - master
+    - pegen
     - /^\d\.\d+$/
     - buildbot-custom
 
@@ -157,7 +158,9 @@ install:
 before_script:
   # -Og is much faster than -O0
   - CFLAGS="${CFLAGS} -Og" ./configure --with-pydebug
-  - make -j4 regen-all
+  - eval "$(pyenv init -)"
+  - pyenv global 3.8
+  - PYTHON_FOR_REGEN=python3.8 make -j4 regen-all
   - changes=`git status --porcelain`
   - |
       # Check for changes in regenerated files
diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst
--- a/Doc/using/cmdline.rst
+++ b/Doc/using/cmdline.rst
@@ -426,6 +426,8 @@ Miscellaneous options
    defines the following possible values:
 
    * ``-X faulthandler`` to enable :mod:`faulthandler`;
+   * ``-X oldparser``: enable the traditional LL(1) parser.  See also
+     :envvar:`PYTHONOLDPARSER`.
    * ``-X showrefcount`` to output the total reference count and number of used
      memory blocks when the program finishes or after each statement in the
      interactive interpreter. This only works on debug builds.
@@ -574,6 +576,12 @@ conflict.
    :option:`-d` multiple times.
 
 
+.. envvar:: PYTHONOLDPARSER
+
+   If this is set it is equivalent to specifying the :option:`-X`
+   ``oldparser`` option.
+
+
 .. envvar:: PYTHONINSPECT
 
    If this is set to a non-empty string it is equivalent to specifying the
diff --git a/"Misc/NEWS.d/next/Core and Builtins/2020-04-20-14-06-19.bpo-40334.CTLGEp.rst" b/"Misc/NEWS.d/next/Core and Builtins/2020-04-20-14-06-19.bpo-40334.CTLGEp.rst"
new file mode 100644
--- /dev/null
+++ b/"Misc/NEWS.d/next/Core and Builtins/2020-04-20-14-06-19.bpo-40334.CTLGEp.rst"
@@ -0,0 +1,5 @@
+Switch to a new parser, based on PEG.  For more details see PEP 617. To
+temporarily switch back to the old parser, use ``-X oldparser`` or
+``PYTHONOLDPARSER=1``.  In Python 3.10 we will remove the old parser
+completely, including the ``parser`` module (already deprecated) and
+anything that depends on it.
diff --git a/Tools/README b/Tools/README
--- a/Tools/README
+++ b/Tools/README
@@ -23,6 +23,8 @@ msi             Support for packaging Python as an MSI package on Windows.
 
 parser          Un-parsing tool to generate code from an AST.
 
+peg_generator   PEG-based parser generator (pegen) used for new parser.
+
 pynche          A Tkinter-based color editor.
 
 scripts         A number of useful single-file programs, e.g. tabnanny.py
diff --git a/Tools/peg_generator/data/xxl.zip b/Tools/peg_generator/data/xxl.zip
new file mode 100644
--- /dev/null
+++ b/Tools/peg_generator/data/xxl.zip