diff --git a/extra/sequences/interleaved/authors.txt b/extra/sequences/interleaved/authors.txt
new file mode 100644
index 0000000000..e091bb8164
--- /dev/null
+++ b/extra/sequences/interleaved/authors.txt
@@ -0,0 +1 @@
+John Benediktsson
diff --git a/extra/sequences/interleaved/interleaved-tests.factor b/extra/sequences/interleaved/interleaved-tests.factor
new file mode 100644
index 0000000000..1091117cd6
--- /dev/null
+++ b/extra/sequences/interleaved/interleaved-tests.factor
@@ -0,0 +1,7 @@
+USING: sequences.interleaved strings tools.test ;
+
+{ "" } [ "" CHAR: _ <interleaved> >string ] unit-test
+{ "a" } [ "a" CHAR: _ <interleaved> >string ] unit-test
+{ "a_b" } [ "ab" CHAR: _ <interleaved> >string ] unit-test
+{ "a_b_c" } [ "abc" CHAR: _ <interleaved> >string ] unit-test
+{ "a_b_c_d" } [ "abcd" CHAR: _ <interleaved> >string ] unit-test
diff --git a/extra/sequences/interleaved/interleaved.factor b/extra/sequences/interleaved/interleaved.factor
new file mode 100644
index 0000000000..680f971711
--- /dev/null
+++ b/extra/sequences/interleaved/interleaved.factor
@@ -0,0 +1,26 @@
+! Copyright (C) 2018 John Benediktsson.
+! See http://factorcode.org/license.txt for BSD license.
+
+USING: accessors kernel math math.order sequences
+sequences.private ;
+
+IN: sequences.interleaved
+
+TUPLE: interleaved { seq read-only } { elt read-only } ;
+
+C: <interleaved> interleaved
+
+M: interleaved length seq>> length dup 1 - + 0 max ;
+
+M: interleaved nth-unsafe
+    over even? [
+        [ 2 / ] [ seq>> ] bi* nth-unsafe
+    ] [
+        nip elt>>
+    ] if ;
+
+M: interleaved like seq>> like ;
+
+M: interleaved new-sequence seq>> new-sequence ;
+
+INSTANCE: interleaved immutable-sequence
diff --git a/extra/sequences/interleaved/summary.txt b/extra/sequences/interleaved/summary.txt
new file mode 100644
index 0000000000..7340d3d93c
--- /dev/null
+++ b/extra/sequences/interleaved/summary.txt
@@ -0,0 +1 @@
+Interleaved sequences