diff --git a/problems/12-integer-to-roman/main.rb b/problems/12-integer-to-roman/main.rb
new file mode 100644
index 0000000..9b0034b
--- /dev/null
+++ b/problems/12-integer-to-roman/main.rb
@@ -0,0 +1,32 @@
+# @param {Integer} num
+# @return {String}
+def int_to_roman(num)
+  res = ''
+
+  if num >= 1000
+    res += 'M' * (num / 1000)
+    num %= 1000
+  end
+
+  if num >= 100
+    res += to_roman(num / 100, 'C', 'D', 'M')
+    num %= 100
+  end
+
+  if num >= 10
+    res += to_roman(num / 10, 'X', 'L', 'C')
+    num %= 10
+  end
+
+  res + to_roman(num, 'I', 'V', 'X')
+end
+
+def to_roman(num, one, five, ten)
+  return one * num if num <= 3
+
+  return one + five if num == 4
+
+  return five + one * (num - 5) if num <= 8
+
+  one + ten
+end
diff --git a/problems/12-integer-to-roman/test.rb b/problems/12-integer-to-roman/test.rb
new file mode 100644
index 0000000..903cf50
--- /dev/null
+++ b/problems/12-integer-to-roman/test.rb
@@ -0,0 +1,24 @@
+require_relative 'main'
+require 'test/unit'
+
+class TestIntegerToRoman < Test::Unit::TestCase
+  def test_simple_integer
+    assert_equal('III', int_to_roman(3))
+  end
+
+  def test_complex_integer
+    assert_equal('LVIII', int_to_roman(58))
+  end
+
+  def test_substaction
+    assert_equal('MCMXCIV', int_to_roman(1994))
+  end
+
+  def test_smallest_number
+    assert_equal('I', int_to_roman(1))
+  end
+
+  def test_largest_number
+    assert_equal('MMMCMXCIX', int_to_roman(3999))
+  end
+end