diff --git a/nox/tox4_to_nox.jinja2 b/nox/tox4_to_nox.jinja2
new file mode 100644
index 00000000..e5a67d9b
--- /dev/null
+++ b/nox/tox4_to_nox.jinja2
@@ -0,0 +1,33 @@
+import nox
+
+{% for envname, envconfig in config.items()|sort: %}
+@nox.session({%- if envconfig.base_python %}python='{{envconfig.base_python}}'{%- endif %})
+def {{fixname(envname)}}(session):
+    {%- if envconfig.description != '' %}
+    """{{envconfig.description}}"""
+    {%- endif %}
+    {%- set envs = envconfig.get('set_env', {}) -%}
+    {%- for key, value in envs.items()|sort: %}
+    session.env['{{key}}'] = '{{value}}'
+    {%- endfor %}
+
+    {%- if envconfig.deps %}
+    session.install({{envconfig.deps}})
+    {%- endif %}
+
+    {%- if not envconfig.skip_install %}
+    {%- if envconfig.use_develop %}
+    session.install('-e', '.')
+    {%- else %}
+    session.install('.')
+    {%- endif -%}
+    {%- endif %}
+
+    {%- if envconfig.change_dir %}
+    session.chdir('{{envconfig.change_dir}}')
+    {%- endif %}
+
+    {%- for command in envconfig.commands %}
+    session.run({{command}})
+    {%- endfor %}
+{% endfor %}
diff --git a/nox/tox_to_nox.py b/nox/tox_to_nox.py
index a6591b4b..866027a8 100644
--- a/nox/tox_to_nox.py
+++ b/nox/tox_to_nox.py
@@ -17,16 +17,30 @@
 from __future__ import annotations
 
 import argparse
+import os
 import pkgutil
+import re
+from configparser import ConfigParser
+from pathlib import Path
+from subprocess import check_output
 from typing import Any, Iterator
 
 import jinja2
 import tox.config
+from tox import __version__ as TOX_VERSION
 
-_TEMPLATE = jinja2.Template(
-    pkgutil.get_data(__name__, "tox_to_nox.jinja2").decode("utf-8"),  # type: ignore[union-attr]
-    extensions=["jinja2.ext.do"],
-)
+TOX4 = TOX_VERSION[0] == "4"
+
+if TOX4:
+    _TEMPLATE = jinja2.Template(
+        pkgutil.get_data(__name__, "tox4_to_nox.jinja2").decode("utf-8"),  # type: ignore[union-attr]
+        extensions=["jinja2.ext.do"],
+    )
+else:
+    _TEMPLATE = jinja2.Template(
+        pkgutil.get_data(__name__, "tox_to_nox.jinja2").decode("utf-8"),  # type: ignore[union-attr]
+        extensions=["jinja2.ext.do"],
+    )
 
 
 def wrapjoin(seq: Iterator[Any]) -> str:
@@ -34,7 +48,7 @@ def wrapjoin(seq: Iterator[Any]) -> str:
 
 
 def fixname(envname: str) -> str:
-    envname = envname.replace("-", "_")
+    envname = envname.replace("-", "_").replace("testenv:", "")
     if not envname.isidentifier():
         print(
             f"Environment {envname!r} is not a valid nox session name.\n"
@@ -49,7 +63,64 @@ def main() -> None:
 
     args = parser.parse_args()
 
-    config = tox.config.parseconfig([])
+    if TOX4:
+        output = check_output(["tox", "config"], text=True)
+        original_config = ConfigParser()
+        original_config.read_string(output)
+        config = {}
+
+        for name, section in original_config.items():
+            if name == "DEFAULT":
+                continue
+
+            config[name] = dict(section)
+            # Convert set_env from string to dict
+            set_env = {}
+            for var in section.get("set_env", "").strip().splitlines():
+                k, v = var.split("=")
+                if k not in (
+                    "PYTHONHASHSEED",
+                    "PIP_DISABLE_PIP_VERSION_CHECK",
+                    "PYTHONIOENCODING",
+                ):
+                    set_env[k] = v
+
+            config[name]["set_env"] = set_env
+
+            if isinstance(section.get("commands"), str):
+                config[name]["commands"] = [
+                    wrapjoin(c.split())
+                    for c in section["commands"].strip().splitlines()
+                ]
+
+            if isinstance(section.get("deps"), str):
+                config[name]["deps"] = wrapjoin(section["deps"].strip().splitlines())
+
+            for option in "skip_install", "use_develop":
+                if section.get(option):
+                    if section[option] == "False":
+                        config[name][option] = False
+                    else:
+                        config[name][option] = True
+
+            if os.path.isabs(section["base_python"]) or re.match(
+                r"py\d+", section["base_python"]
+            ):
+                impl = (
+                    "python" if section["py_impl"] == "cpython" else section["py_impl"]
+                )
+                config[name]["base_python"] = impl + section["py_dot_ver"]
+
+            change_dir = Path(section.get("change_dir"))
+            rel_to_cwd = change_dir.relative_to(Path.cwd())
+            if str(rel_to_cwd) == ".":
+                config[name]["change_dir"] = None
+            else:
+                config[name]["change_dir"] = rel_to_cwd
+
+    else:
+        config = tox.config.parseconfig([])
+
     output = _TEMPLATE.render(config=config, wrapjoin=wrapjoin, fixname=fixname)
 
     with open(args.output, "w") as outfile:
diff --git a/noxfile.py b/noxfile.py
index 45a98736..eecc0e6d 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -46,6 +46,17 @@ def tests(session: nox.Session) -> None:
         *session.posargs,
         env={"COVERAGE_FILE": f".coverage.{session.python}"},
     )
+    # Test tox_to_nox with older tox
+    session.install("tox<4")
+    session.run(
+        "pytest",
+        "--cov=nox",
+        "--cov-config",
+        "pyproject.toml",
+        "--cov-report=",
+        "tests/test_tox_to_nox.py",
+        env={"COVERAGE_FILE": f".coverage.{session.python}.tox3"},
+    )
     session.notify("cover")
 
 
diff --git a/pyproject.toml b/pyproject.toml
index f9b8ea88..bc6d449c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -50,7 +50,7 @@ classifiers = [
 [project.optional-dependencies]
 tox_to_nox = [
   "jinja2",
-  "tox<4",
+  "tox",
 ]
 
 [project.urls]
diff --git a/tests/test_tox_to_nox.py b/tests/test_tox_to_nox.py
index c7b54850..47a2770f 100644
--- a/tests/test_tox_to_nox.py
+++ b/tests/test_tox_to_nox.py
@@ -18,9 +18,12 @@
 import textwrap
 
 import pytest
+from tox import __version__ as TOX_VERSION
 
 from nox import tox_to_nox
 
+TOX4 = TOX_VERSION[0] == "4"
+
 
 @pytest.fixture
 def makeconfig(tmpdir):
@@ -277,6 +280,7 @@ def test_with_dash(session):
     )
 
 
+@pytest.mark.skipif(TOX4, reason="Not supported in tox 4.")
 def test_non_identifier_in_envname(makeconfig, capfd):
     result = makeconfig(
         textwrap.dedent(