diff --git a/dnstapir/dns/__init__.py b/dnstapir/dns/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/dnstapir/dns/mozpsl.py b/dnstapir/dns/mozpsl.py
new file mode 100644
index 0000000..9edd97b
--- /dev/null
+++ b/dnstapir/dns/mozpsl.py
@@ -0,0 +1,142 @@
+import io
+from typing import Self
+
+import httpx
+
+
+class TrieNode:
+    """ "Storage class for Trie"""
+
+    def __init__(self) -> None:
+        self.count = 0
+        self.icann: bool | None = None
+        self.children: dict[str, Self] = {}
+
+
+class Trie:
+    def __init__(self) -> None:
+        self.root = TrieNode()
+
+    def __repr__(self) -> str:
+        """Print full Trie structure"""
+
+        def recur(node: TrieNode, indent: str) -> str:
+            return "".join(
+                indent + key + (f" {child.count}" if child.count else "") + recur(child, indent + " - ")
+                for key, child in node.children.items()
+            )
+
+        return recur(self.root, "\n")
+
+    def insert(self, array: list[str], nlbl: int, icann: bool) -> None:
+        """Add data to Trie"""
+        node = self.root
+        for x in array:
+            if x in node.children:
+                node = node.children[x]
+            else:
+                child = TrieNode()
+                node.children[x] = child
+                node = child
+        node.count = nlbl
+        node.icann = icann
+
+    def search(self, key: list[str]) -> tuple[int, int]:
+        """Search Trie"""
+        core = 0
+        pcore = 0
+        current = self.root
+        for label in key:
+            if current.icann is True:
+                core = current.count
+            elif current.icann is False:
+                pcore = current.count
+            # # If current.icann is None, do not update core or pcore
+            if label not in current.children:
+                if current.count != 0:
+                    break
+                else:
+                    raise KeyError
+            current = current.children[label]
+        if pcore == core:
+            pcore = 0
+        return (core, pcore)
+
+
+class PublicSuffixList:
+    """Mozilla Public Suffix List"""
+
+    def __init__(self) -> None:
+        self.trie = Trie()
+
+    def load_psl_url(self, url: str) -> None:
+        """Load PSL from URL"""
+        response = httpx.get(
+            url,
+            headers={
+                "Accept-Encoding": "gzip",
+            },
+        )
+        response.raise_for_status()
+        self.load_psl(io.StringIO(response.text))
+
+    def load_psl(self, stream: io.StringIO) -> None:
+        """Load PSL from stream"""
+        icann = False
+        for line in stream:
+            line = line.rstrip()
+
+            if "===BEGIN ICANN DOMAINS===" in line:
+                # Mark ICANN domains
+                icann = True
+            elif "===BEGIN PRIVATE DOMAINS===" in line:
+                # Mark PRIVATE domains
+                icann = False
+
+            if (line.strip() == "") or (line[0] == "/"):
+                # Remove empty or comment lines
+                continue
+
+            # Set number of labels in core domain
+            labels = len(line.split(".")) + 1
+
+            # Wildcards
+            if line[0] == "*":
+                line = line[2:]
+
+            # Exclusions... .ck and .jp, just stop
+            if line[0] == "!":
+                line = line[1:]
+                labels -= 2
+
+            # Convert from Unicode
+            lbls = line.encode("idna").decode().split(".")
+
+            # Store reversed
+            lbls.reverse()
+
+            # Insert into Trie
+            self.trie.insert(lbls, labels, icann)
+
+    def coredomain(self, domain: str) -> tuple[str, str]:
+        """Find ICANN and private name cut-off for domain"""
+        if not domain:
+            raise ValueError
+        try:
+            domain = domain.rstrip(".")
+        except AttributeError as exc:
+            raise ValueError from exc
+        lbls = domain.split(".")
+        lbls.reverse()
+        c, p = self.trie.search(lbls)
+        core = lbls[0:c]
+        core.reverse()
+        pcore = lbls[0:p]
+        pcore.reverse()
+        return (".".join(core), ".".join(pcore))
+
+    def rdomain(self, rdomain: str) -> tuple[str, str]:
+        """Find ICANN and private name cut-off for domain, reverse order process"""
+        lbls = rdomain.split(".")
+        c, p = self.trie.search(lbls)
+        return (".".join(lbls[0:c]), ".".join(lbls[0:p]))
diff --git a/poetry.lock b/poetry.lock
index ada2644..2575a40 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -330,20 +330,20 @@ test-randomorder = ["pytest-randomly"]
 
 [[package]]
 name = "deprecated"
-version = "1.2.14"
+version = "1.2.15"
 description = "Python @deprecated decorator to deprecate old python classes, functions or methods."
 optional = true
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,>=2.7"
 files = [
-    {file = "Deprecated-1.2.14-py2.py3-none-any.whl", hash = "sha256:6fac8b097794a90302bdbb17b9b815e732d3c4720583ff1b198499d78470466c"},
-    {file = "Deprecated-1.2.14.tar.gz", hash = "sha256:e5323eb936458dccc2582dc6f9c322c852a775a27065ff2b0c4970b9d53d01b3"},
+    {file = "Deprecated-1.2.15-py2.py3-none-any.whl", hash = "sha256:353bc4a8ac4bfc96800ddab349d89c25dec1079f65fd53acdcc1e0b975b21320"},
+    {file = "deprecated-1.2.15.tar.gz", hash = "sha256:683e561a90de76239796e6b6feac66b99030d2dd3fcf61ef996330f14bbb9b0d"},
 ]
 
 [package.dependencies]
 wrapt = ">=1.10,<2"
 
 [package.extras]
-dev = ["PyTest", "PyTest-Cov", "bump2version (<1)", "sphinx (<2)", "tox"]
+dev = ["PyTest", "PyTest-Cov", "bump2version (<1)", "jinja2 (>=3.0.3,<3.1.0)", "setuptools", "sphinx (<2)", "tox"]
 
 [[package]]
 name = "dnspython"
diff --git a/tests/test_dns_mozpsl.py b/tests/test_dns_mozpsl.py
new file mode 100644
index 0000000..f79cd0f
--- /dev/null
+++ b/tests/test_dns_mozpsl.py
@@ -0,0 +1,37 @@
+import pytest
+
+from dnstapir.dns.mozpsl import PublicSuffixList
+
+MOZ_PSL = "https://publicsuffix.org/list/public_suffix_list.dat"
+
+
+def test_mozpsl():
+    psl = PublicSuffixList()
+    psl.load_psl_url(url=MOZ_PSL)
+
+    assert psl.coredomain("www.ck.") == ("www.ck", "")
+    assert psl.coredomain("www.something.gov.ck.") == ("something.gov.ck", "")
+    assert psl.coredomain("www.something.or.other.microsoft.com.") == ("microsoft.com", "")
+    assert psl.coredomain("www.something.or.other.microsoft.com.br.") == ("microsoft.com.br", "")
+    assert psl.coredomain("www.something.emrstudio-prod.us-gov-east-1.amazonaws.com.") == (
+        "amazonaws.com",
+        "something.emrstudio-prod.us-gov-east-1.amazonaws.com",
+    )
+    assert psl.rdomain("com.amazonaws.us-gov-east-1.emrstudio-prod.www.something.emrstudio-prod") == (
+        "com.amazonaws",
+        "com.amazonaws.us-gov-east-1.emrstudio-prod.www",
+    )
+
+    with pytest.raises(KeyError):
+        psl.coredomain("local.")
+
+    # IDN test
+    assert psl.coredomain("www.xn--mnchen-3ya.de.") == ("xn--mnchen-3ya.de", "")
+
+    # Edge cases
+    with pytest.raises(ValueError):
+        psl.coredomain("")
+    with pytest.raises(ValueError):
+        psl.coredomain(None)
+    with pytest.raises(KeyError):
+        psl.coredomain("invalid..domain.")