diff --git a/chrono/utils/interval.py b/chrono/utils/interval.py
index 2a17ecff..2b49b203 100644
--- a/chrono/utils/interval.py
+++ b/chrono/utils/interval.py
@@ -15,9 +15,35 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import bisect
-import collections
+import typing
 
-Interval = collections.namedtuple('Interval', ['begin', 'end'])
+
+class Interval(typing.NamedTuple):
+    begin: typing.Any
+    end: typing.Any
+
+    def disjoint(self, other):
+        return self < other or self > other
+
+    def overlaps(self, other):
+        return not self.disjoint(other)
+
+    def __lt__(self, other):
+        return self[1] < other[0]
+
+    def __gt__(self, other):
+        return other[1] < self[0]
+
+    def union(self, other):
+        other = self.cast(other)
+        assert self.overlaps(other)
+        return Interval(min(self.begin, other.begin), max(self.end, other.end))
+
+    @classmethod
+    def cast(cls, other):
+        if isinstance(other, cls):
+            return other
+        return cls(*other)
 
 
 class IntervalSet:
@@ -159,6 +185,9 @@ class IntervalSet:
             return value
         return cls(value)
 
+    def __rsub__(self, other):
+        return self.cast(other) - self
+
     def __sub__(self, other):
         l1 = iter(self)
         l2 = iter(self.cast(other))
@@ -200,6 +229,95 @@ class IntervalSet:
 
         return self.__class__.from_ordered(gen())
 
+    def __radd__(self, other):
+        return self.cast(other).__add__(self)
+
+    def __add__(self, other):
+        l1 = iter(self)
+        l2 = iter(self.cast(other))
+
+        def gen():
+            state = 3
+            current = None
+            while True:
+                if state & 1:
+                    c1 = next(l1, None)
+                if state & 2:
+                    c2 = next(l2, None)
+                if current:
+                    if not c1 and not c2:
+                        yield current
+                        break
+                    if not c1:
+                        if current < c2:
+                            yield current
+                            yield c2
+                            break
+                        if c2 < current:
+                            yield c2
+                            yield current
+                        else:
+                            yield current.union(c2)
+                            break
+                    if not c2:
+                        if current < c1:
+                            yield current
+                            yield c1
+                            break
+                        if c1 < current:
+                            yield c1
+                            yield current
+                        else:
+                            yield current.union(c1)
+                            break
+                    if current < c1 and current < c2:
+                        yield current
+                        current = None
+                    elif current.overlaps(c1) and current.overlaps(c2):
+                        yield current.union(c1).union(c2)
+                        current = None
+                        state = 3
+                        continue
+                    elif current < c2:
+                        yield current.union(c1)
+                        current = None
+                        state = 1
+                        continue
+                    else:
+                        yield current.union(c2)
+                        current = None
+                        state = 2
+                        continue
+                if not c1 and not c2:
+                    # l1 and l2 are empty, stop
+                    break
+                if not c1:
+                    # l1 is empty, yield c2 and stop
+                    yield c2
+                    break
+                if not c2:
+                    # l2 is empty, yield c1 and stop
+                    yield c1
+                    break
+                if c1 < c2:
+                    # l1 is before l2, yield c1 and advance l1 only
+                    yield c1
+                    state = 1
+                    continue
+                if c2 < c1:
+                    # l2 is before l1, yield c2 and advance l2 only
+                    yield c2
+                    state = 2
+                    continue
+                current = c1.union(c2)
+                state = 3
+
+            # finish by yielding from the not empty ones
+            yield from l1
+            yield from l2
+
+        return self.__class__.from_ordered(gen())
+
     def min(self):
         if self:
             return self.begin[0]
diff --git a/tests/test_interval.py b/tests/test_interval.py
index 04a53bf5..b27e8d0b 100644
--- a/tests/test_interval.py
+++ b/tests/test_interval.py
@@ -3,6 +3,11 @@ import pytest
 from chrono.utils.interval import Interval, IntervalSet
 
 
+def test_interval_union():
+    assert Interval(1, 2).union((2, 3)) == (1, 3)
+    assert Interval(1, 2).union((2, 3)) == Interval(1, 3)
+
+
 def test_interval_set_merge_adjacent():
     """
     Test that adjacent intervals are merged
@@ -67,6 +72,8 @@ def test_interval_set_sub():
     assert (s - []) == s
     assert (IntervalSet([(0, 2)]) - [(1, 2)]) == [(0, 1)]
 
+    assert ([] - s) == []
+
 
 def test_interval_set_min_max():
     assert IntervalSet().min() is None
@@ -86,3 +93,25 @@ def test_interval_set_eq():
     assert not IntervalSet([(1, 2)]) == None  # noqa pylint: disable=singleton-comparison
     # noqa pylint: disable=singleton-comparison
     assert not None == IntervalSet([(1, 2)])
+
+
+def test_interval_set_add():
+    s = IntervalSet([(0, 3), (4, 7), (8, 11), (12, 15)])
+    t = IntervalSet([(3, 4), (7, 8), (11, 12)])
+
+    assert s + t == [(0, 15)]
+    assert t + s == [(0, 15)]
+    assert [(3, 4), (7, 8), (11, 12)] + s == [(0, 15)]
+
+    t = IntervalSet([(3, 4), (11, 12)])
+    assert s + t == [(0, 7), (8, 15)]
+    assert t + s == [(0, 7), (8, 15)]
+
+    t = IntervalSet([(2, 5), (10, 13)])
+    assert s + t == [(0, 7), (8, 15)]
+    assert t + s == [(0, 7), (8, 15)]
+
+    assert s + [] == s
+    assert [] + s == s
+
+    assert IntervalSet([(1, 3), (4, 6)]) + [(3, 4), (4, 5)] == [(1, 6)]