diff --git a/setup.cfg b/setup.cfg
index 217c8ee..d716b0e 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -40,6 +40,11 @@ packages = find:
 python_requires = >=3.8
 install_requires =
   python-dateutil
+  lark
+
+[options.package_data]
+* =
+    *.lark
 
 [options.extras_require]
 all =
diff --git a/src/undate/dateformat/edtf/__init__.py b/src/undate/dateformat/edtf/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/undate/dateformat/edtf/edtf.lark b/src/undate/dateformat/edtf/edtf.lark
new file mode 100644
index 0000000..6b8e5aa
--- /dev/null
+++ b/src/undate/dateformat/edtf/edtf.lark
@@ -0,0 +1,64 @@
+%import common.ESCAPED_STRING   -> STRING
+%import common.INT -> INT
+%import common.WS
+%ignore WS
+
+// --- EDTF / ISO 8601-2 ---
+
+?edtf: edtf_level0 | edtf_level1
+
+// --- EDTF Level 0 / ISO 8601-1 ---
+
+?edtf_level0: date | timeinterval
+// not implementing datetime for now
+
+date: year | year "-" month | year "-" month "-" day
+
+year: INT
+month: /(0[1-9])|(1[0-2])/
+day: /([0-2][1-9])|(3[0-1])/
+
+timeinterval: date "/" date
+
+
+// EDTF Level 1
+
+?edtf_level1: date_level1 | extended_interval
+
+// qualification may occur at the end of the date
+qualification: uncertain | approximate | uncertain_approximate
+
+uncertain: "?"
+approximate: "~"
+uncertain_approximate: "%"
+
+// The character 'X' may be used in place of one or more rightmost
+// digits to indicate that the value of that digit is unspecified
+unspecified: /X/
+?year_unspecified: /\d+/ unspecified+
+?month_unspecified: "0".."1"? unspecified ~ 1..2
+//?year_month_unspecified: year_l1 "-" month_unspecified
+?day_unspecified: "0".."3"? unspecified ~ 1..2
+
+// 'Y' may be used at the beginning of the date string to signify that the date is a year, when (and only when) the year exceeds four digits, i.e. for years later than 9999 or earlier than -9999.
+year_fivedigitsplus: /Y\d{5,}/
+?year_l1: year_fivedigitsplus | year | year_unspecified
+
+// The values 21, 22, 23, 24 may be used used to signify
+// ' Spring', 'Summer', 'Autumn', 'Winter', respectively,
+// in place of a month value (01 through 12) for a year-and-month format string.
+season: /2[1-4]/
+?year_season: year_l1 "-" season
+
+date_level1: (year_l1
+	| year_l1 "-" (month | month_unspecified)
+	| year_l1 "-" (month | month_unspecified) "-" (day | day_unspecified)
+	| year_season) qualification?
+
+// unknown date:  double dot or empty string
+unknown_date: ".."?
+extended_interval: date_level1 "/" date_level1
+	| date_level1 "/" unknown_date
+	| unknown_date "/" date_level1
+
+// negative calendar year?
\ No newline at end of file
diff --git a/src/undate/dateformat/edtf/parser.py b/src/undate/dateformat/edtf/parser.py
new file mode 100644
index 0000000..8826b2d
--- /dev/null
+++ b/src/undate/dateformat/edtf/parser.py
@@ -0,0 +1,46 @@
+import os.path
+
+from lark import Lark
+
+
+grammar_path = os.path.join(os.path.dirname(__file__), "edtf.lark")
+
+with open(grammar_path) as grammar:
+    edtf_parser = Lark(grammar.read(), start="edtf")
+
+
+# testcases = [
+#     "1984",
+#     "1984-05",
+#     "1984-12",
+#     "1001-03-30",
+#     "1000/2000",
+#     "1000-01/2000-05-01",
+#     # level 1
+#     "Y170000002",
+#     "2001-21",  # spring 2001
+#     # qualifiers
+#     "1984?",
+#     "2004-06~",
+#     "2004-06-11%",
+#     # unspecified digits from right
+#     "201X",
+#     "20XX",
+#     "2004-XX",
+#     "1985-04-XX",
+#     "1985-XX-XX",
+#     # open ended intervals
+#     "1985-04-12/..",
+#     "1985-04/..",
+#     "../1985-04-12",
+#     "/1985-04-12",
+#     "1984-13",
+# ]
+
+# for testcase in testcases:
+#     print(f"\n{testcase}")
+#     tree = edtf_parser.parse(testcase)
+#     print(tree.pretty())
+
+
+# error_cases = ["1984-13", "Y1702"]
diff --git a/src/undate/dateformat/edtf/transformer.py b/src/undate/dateformat/edtf/transformer.py
new file mode 100644
index 0000000..cca3609
--- /dev/null
+++ b/src/undate/dateformat/edtf/transformer.py
@@ -0,0 +1,70 @@
+from lark import Transformer, Tree, Token
+from undate.undate import Undate, UndateInterval
+
+
+class EDTFTransformer(Transformer):
+    """transform edtf parse tree and return Undate or UndateInterval"""
+
+    INT = int
+
+    def timeinterval(self, items):
+        # transformed result from parser should be two undate objects;
+        # combine into an interval
+        return UndateInterval(*items)
+
+    def date(self, items):
+        parts = {}
+        for child in items:
+            if child.data in ["year", "month", "day"]:
+                # in each case we expect one value;
+                # anonymous tokens convert to their value
+                value = child.children[0]
+                # convert to integer when possible; otherwise pass as string
+                try:
+                    value = int(value)
+                except ValueError:
+                    value = str(value)
+                parts[str(child.data)] = value
+
+        return Undate(**parts)
+
+    def extended_interval(self, items):
+        # same as level 1 time interval, except one item may be None
+        # for an open-ended range
+        return self.timeinterval(items)
+
+    def unknown_date(self, token):
+        # unknown date for interval should be passed in as None
+        return None
+
+    def get_values(self, items):
+        # get a list of values from tokens; recurses to get subtree tokens
+        values = []
+        for i in items:
+            if isinstance(i, Token):
+                values.append(str(i))
+            if isinstance(i, Tree):
+                values.extend(self.get_values(i.children))
+        return values
+
+    def year_unspecified(self, items):
+        # combine parts (numeric & unknown) into a single string
+        value = "".join(self.get_values(items))
+        return Tree(data="year", children=[value])
+
+    def month_unspecified(self, items):
+        value = "".join(self.get_values(items))
+        return Tree(data="month", children=[value])
+
+    def day_unspecified(self, items):
+        value = "".join(self.get_values(items))
+        return Tree(data="day", children=[value])
+
+    def date_level1(self, items):
+        return self.date(items)
+
+    def year_fivedigitsplus(self, token):
+        # strip off the leading Y and convert to integer
+        # TODO: undate is currently limited to 4-digit years
+        # (datetime max year of 9999)
+        return tok.update(int(token[:1]))
diff --git a/tests/test_dateformat/edtf/test_edtf_parser.py b/tests/test_dateformat/edtf/test_edtf_parser.py
new file mode 100644
index 0000000..5a2b8ea
--- /dev/null
+++ b/tests/test_dateformat/edtf/test_edtf_parser.py
@@ -0,0 +1,46 @@
+import pytest
+
+from undate.dateformat.edtf.parser import edtf_parser
+
+# for now, just test that valid dates can be parsed
+
+testcases = [
+    "1984",
+    "1984-05",
+    "1984-12",
+    "1001-03-30",
+    "1000/2000",
+    "1000-01/2000-05-01",
+    # level 1
+    "Y170000002",
+    "2001-21",  # spring 2001
+    # qualifiers
+    "1984?",
+    "2004-06~",
+    "2004-06-11%",
+    # unspecified digits from right
+    "201X",
+    "20XX",
+    "2004-XX",
+    "1985-04-XX",
+    "1985-XX-XX",
+    # open ended intervals
+    "1985-04-12/..",
+    "1985-04/..",
+    "../1985-04-12",
+    "/1985-04-12",
+]
+
+
+@pytest.mark.parametrize("date_string", testcases)
+def test_should_parse(date_string):
+    assert edtf_parser.parse(date_string)
+
+
+error_cases = ["1984-13", "Y1702"]
+
+
+@pytest.mark.parametrize("date_string", error_cases)
+def test_should_error(date_string):
+    with pytest.raises(Exception):
+        edtf_parser.parse(date_string)
diff --git a/tests/test_dateformat/edtf/test_edtf_transformer.py b/tests/test_dateformat/edtf/test_edtf_transformer.py
new file mode 100644
index 0000000..8dba34d
--- /dev/null
+++ b/tests/test_dateformat/edtf/test_edtf_transformer.py
@@ -0,0 +1,44 @@
+import pytest
+
+from undate.undate import Undate, UndateInterval
+from undate.dateformat.edtf.parser import edtf_parser
+from undate.dateformat.edtf.transformer import EDTFTransformer
+
+# for now, just test that valid dates can be parsed
+
+testcases = [
+    ("1984", Undate(1984)),
+    ("1984-05", Undate(1984, 5)),
+    ("1984-12", Undate(1984, 12)),
+    ("1001-03-30", Undate(1001, 3, 30)),
+    ("1000/2000", UndateInterval(Undate(1000), Undate(2000))),
+    ("1000-01/2000-05-01", UndateInterval(Undate(1000, 1), Undate(2000, 5, 1))),
+    # # level 1
+    # NOTE: undate currently doesn't most of the level 1 functionality
+    # NOTE: undate currently doesn't support years beyond 9999 (datetime.MAXYEAR)
+    # ("Y17000002", Undate(17000002)),
+    # "2001-21",  # spring 2001
+    # # qualifiers
+    # "1984?",
+    # "2004-06~",
+    # "2004-06-11%",
+    # # unspecified digits from right
+    ("201X", Undate("201X")),
+    ("20XX", Undate("20XX")),
+    ("2004-XX", Undate(2004, "XX")),
+    ("1985-04-XX", Undate(1985, 4, "XX")),
+    ("1985-XX-XX", Undate(1985, "XX", "XX")),
+    # # open ended intervals
+    ("1985-04-12/..", UndateInterval(Undate(1985, 4, 12), None)),
+    ("1985-04/..", UndateInterval(Undate(1985, 4), None)),
+    ("../1985-04-12", UndateInterval(None, Undate(1985, 4, 12))),
+    ("/1985-04-12", UndateInterval(None, Undate(1985, 4, 12))),
+]
+
+
+@pytest.mark.parametrize("date_string,expected", testcases)
+def test_transform(date_string, expected):
+    transformer = EDTFTransformer()
+    # parse the input string, then transform to undate object
+    parsetree = edtf_parser.parse(date_string)
+    assert transformer.transform(parsetree) == expected
diff --git a/tests/test_dateformat/test_base.py b/tests/test_dateformat/test_base.py
index 63568f0..3687a37 100644
--- a/tests/test_dateformat/test_base.py
+++ b/tests/test_dateformat/test_base.py
@@ -31,9 +31,12 @@ def test_parse_to_string(self):
             BaseDateFormat().to_string(1991)
 
 
-@pytest.mark.first
 def test_import_formatters_import_only_once(caplog):
-    # run first so we can confirm it runs once
+    # clear the cache, since any instantiation of an Undate
+    # object anywhere in the test suite will populate it
+    BaseDateFormat.import_formatters.cache_clear()
+
+    # run first, and confirm it runs and loads formatters
     with caplog.at_level(logging.DEBUG):
         import_count = BaseDateFormat.import_formatters()
     # should import at least one thing (iso8601)