diff --git a/spec/language/until_spec.rb b/spec/language/until_spec.rb
new file mode 100644
index 000000000..998ffee79
--- /dev/null
+++ b/spec/language/until_spec.rb
@@ -0,0 +1,237 @@
+require_relative '../spec_helper'
+
+# until bool-expr [do]
+#   body
+# end
+#
+# begin
+#   body
+# end until bool-expr
+#
+# expr until bool-expr
+describe "The until expression" do
+  it "runs while the expression is false" do
+    i = 0
+    until i > 9
+      i += 1
+    end
+
+    i.should == 10
+  end
+
+  it "optionally takes a 'do' after the expression" do
+    i = 0
+    until i > 9 do
+      i += 1
+    end
+
+    i.should == 10
+  end
+
+  it "allows body begin on the same line if do is used" do
+    i = 0
+    until i > 9 do i += 1
+    end
+
+    i.should == 10
+  end
+
+  it "executes code in containing variable scope" do
+    i = 0
+    until i == 1
+      a = 123
+      i = 1
+    end
+
+    a.should == 123
+  end
+
+  it "executes code in containing variable scope with 'do'" do
+    i = 0
+    until i == 1 do
+      a = 123
+      i = 1
+    end
+
+    a.should == 123
+  end
+
+  it "returns nil if ended when condition became true" do
+    i = 0
+    until i > 9
+      i += 1
+    end.should == nil
+  end
+
+  it "evaluates the body if expression is empty" do
+    a = []
+    until ()
+      a << :body_evaluated
+      break
+    end
+    a.should == [:body_evaluated]
+  end
+
+  it "stops running body if interrupted by break" do
+    i = 0
+    until i > 9
+      i += 1
+      break if i > 5
+    end
+    i.should == 6
+  end
+
+  it "returns value passed to break if interrupted by break" do
+    until false
+      break 123
+    end.should == 123
+  end
+
+  it "returns nil if interrupted by break with no arguments" do
+    until false
+      break
+    end.should == nil
+  end
+
+  it "skips to end of body with next" do
+    a = []
+    i = 0
+    until (i+=1)>=5
+      next if i==3
+      a << i
+    end
+    a.should == [1, 2, 4]
+  end
+
+  # NATFIXME: Infinite loop
+  xit "restarts the current iteration without reevaluating condition with redo" do
+    a = []
+    i = 0
+    j = 0
+    until (i+=1)>=3
+      a << i
+      j+=1
+      redo if j<3
+    end
+    a.should == [1, 1, 1, 2]
+  end
+end
+
+describe "The until modifier" do
+  it "runs preceding statement while the condition is false" do
+    i = 0
+    i += 1 until i > 9
+    i.should == 10
+  end
+
+  it "evaluates condition before statement execution" do
+    a = []
+    i = 0
+    a << i until (i+=1) >= 3
+    a.should == [1, 2]
+  end
+
+  it "does not run preceding statement if the condition is true" do
+    i = 0
+    i += 1 until true
+    i.should == 0
+  end
+
+  it "returns nil if ended when condition became true" do
+    i = 0
+    (i += 1 until i>9).should == nil
+  end
+
+  it "returns value passed to break if interrupted by break" do
+    (break 123 until false).should == 123
+  end
+
+  it "returns nil if interrupted by break with no arguments" do
+    (break until false).should == nil
+  end
+
+  it "skips to end of body with next" do
+    i = 0
+    j = 0
+    ((i+=1) == 3 ? next : j+=i) until i > 10
+    j.should == 63
+  end
+
+  # NATFIXME: Infinite loop
+  xit "restarts the current iteration without reevaluating condition with redo" do
+    i = 0
+    j = 0
+    (i+=1) == 4 ? redo : j+=i until (i+=1) > 10
+    j.should == 34
+  end
+end
+
+describe "The until modifier with begin .. end block" do
+  it "runs block while the expression is false" do
+    i = 0
+    begin
+      i += 1
+    end until i > 9
+
+    i.should == 10
+  end
+
+  it "stops running block if interrupted by break" do
+    i = 0
+    begin
+      i += 1
+      break if i > 5
+    end until i > 9
+
+    i.should == 6
+  end
+
+  it "returns value passed to break if interrupted by break" do
+    (begin; break 123; end until false).should == 123
+  end
+
+  it "returns nil if interrupted by break with no arguments" do
+    (begin; break; end until false).should == nil
+  end
+
+  it "runs block at least once (even if the expression is true)" do
+    i = 0
+    begin
+      i += 1
+    end until true
+
+    i.should == 1
+  end
+
+  it "evaluates condition after block execution" do
+    a = []
+    i = 0
+    begin
+      a << i
+    end until (i+=1)>=5
+    a.should == [0, 1, 2, 3, 4]
+  end
+
+  it "skips to end of body with next" do
+    a = []
+    i = 0
+    begin
+      next if i==3
+      a << i
+    end until (i+=1)>=5
+    a.should == [0, 1, 2, 4]
+  end
+
+  # NATFIXME: Infinite loop
+  xit "restart the current iteration without reevaluating condition with redo" do
+    a = []
+    i = 0
+    j = 0
+    begin
+      a << i
+      j+=1
+      redo if j<3
+    end until (i+=1)>=3
+    a.should == [0, 0, 0, 1, 2]
+  end
+end
diff --git a/spec/language/while_spec.rb b/spec/language/while_spec.rb
new file mode 100644
index 000000000..e26c3e58e
--- /dev/null
+++ b/spec/language/while_spec.rb
@@ -0,0 +1,349 @@
+require_relative '../spec_helper'
+
+# while bool-expr [do]
+#   body
+# end
+#
+# begin
+#   body
+# end while bool-expr
+#
+# expr while bool-expr
+describe "The while expression" do
+  it "runs while the expression is true" do
+    i = 0
+    while i < 3
+      i += 1
+    end
+    i.should == 3
+  end
+
+  it "optionally takes a 'do' after the expression" do
+    i = 0
+    while i < 3 do
+      i += 1
+    end
+
+    i.should == 3
+  end
+
+  it "allows body begin on the same line if do is used" do
+    i = 0
+    while i < 3 do i += 1
+    end
+
+    i.should == 3
+  end
+
+  it "executes code in containing variable scope" do
+    i = 0
+    while i != 1
+      a = 123
+      i = 1
+    end
+
+    a.should == 123
+  end
+
+  it "executes code in containing variable scope with 'do'" do
+    i = 0
+    while i != 1 do
+      a = 123
+      i = 1
+    end
+
+    a.should == 123
+  end
+
+  it "returns nil if ended when condition became false" do
+    i = 0
+    while i < 3
+      i += 1
+    end.should == nil
+  end
+
+  it "does not evaluate the body if expression is empty" do
+    a = []
+    while ()
+      a << :body_evaluated
+    end
+    a.should == []
+  end
+
+  it "stops running body if interrupted by break" do
+    i = 0
+    while i < 10
+      i += 1
+      break if i > 5
+    end
+    i.should == 6
+  end
+
+  it "stops running body if interrupted by break in a parenthesized element op-assign-or value" do
+    c = true
+    a = []
+    while c
+      a[1] ||=
+        (
+          break if c
+          c = false
+        )
+    end.should be_nil
+  end
+
+  it "stops running body if interrupted by break in a begin ... end element op-assign-or value" do
+    c = true
+    a = []
+    while c
+      a[1] ||= begin
+        break if c
+        c = false
+      end
+    end.should be_nil
+  end
+
+  it "stops running body if interrupted by break in a parenthesized element op-assign value" do
+    c = true
+    a = [1, 2]
+    while c
+      a[1] +=
+        (
+          break if c
+          c = false
+        )
+    end.should be_nil
+    a.should == [1, 2]
+  end
+
+  it "stops running body if interrupted by break in a begin ... end element op-assign value" do
+    c = true
+    a = [1, 2]
+    while c
+      a[1] += begin
+        break if c
+        c = false
+      end
+    end.should be_nil
+    a.should == [1, 2]
+  end
+
+  it "stops running body if interrupted by break with unless in a parenthesized attribute op-assign-or value" do
+    a = mock("attribute assignment break")
+    a.should_receive(:m).twice.and_return(nil)
+    a.should_receive(:m=)
+
+    c = d = true
+    while c
+      a.m ||=
+        (
+          break unless d
+          d = false
+        )
+    end.should be_nil
+  end
+
+  it "stops running body if interrupted by break with unless in a begin ... end attribute op-assign-or value" do
+    a = mock("attribute assignment break")
+    a.should_receive(:m).twice.and_return(nil)
+    a.should_receive(:m=)
+
+    c = d = true
+    while c
+      a.m ||= begin
+        break unless d
+        d = false
+      end
+    end.should be_nil
+  end
+
+  # NATFIXME: This fails until we capture it with a NATFIXME block
+  xit "stops running body if interrupted by break in a parenthesized attribute op-assign-or value" do
+    a = mock("attribute assignment break")
+    a.should_receive(:m).and_return(nil)
+    a.should_not_receive(:m=)
+
+    c = true
+    while c
+      a.m +=
+        (
+          break if c
+          c = false
+        )
+    end.should be_nil
+  end
+
+  # NATFIXME: This fails until we capture it with a NATFIXME block
+  xit "stops running body if interrupted by break in a begin ... end attribute op-assign-or value" do
+    a = mock("attribute assignment break")
+    a.should_receive(:m).and_return(nil)
+    a.should_not_receive(:m=)
+
+    c = true
+    while c
+      a.m += begin
+        break if c
+        c = false
+      end
+    end.should be_nil
+  end
+
+  it "returns value passed to break if interrupted by break" do
+    while true
+      break 123
+    end.should == 123
+  end
+
+  it "returns nil if interrupted by break with no arguments" do
+    while true
+      break
+    end.should == nil
+  end
+
+  it "skips to end of body with next" do
+    a = []
+    i = 0
+    while (i+=1)<5
+      next if i==3
+      a << i
+    end
+    a.should == [1, 2, 4]
+  end
+
+  # NATFIXME: Infinite loop
+  xit "restarts the current iteration without reevaluating condition with redo" do
+    a = []
+    i = 0
+    j = 0
+    while (i+=1)<3
+      a << i
+      j+=1
+      redo if j<3
+    end
+    a.should == [1, 1, 1, 2]
+  end
+end
+
+describe "The while modifier" do
+  it "runs preceding statement while the condition is true" do
+    i = 0
+    i += 1 while i < 3
+    i.should == 3
+  end
+
+  it "evaluates condition before statement execution" do
+    a = []
+    i = 0
+    a << i while (i+=1) < 3
+    a.should == [1, 2]
+  end
+
+  it "does not run preceding statement if the condition is false" do
+    i = 0
+    i += 1 while false
+    i.should == 0
+  end
+
+  it "does not run preceding statement if the condition is empty" do
+    i = 0
+    i += 1 while ()
+    i.should == 0
+  end
+
+  it "returns nil if ended when condition became false" do
+    i = 0
+    (i += 1 while i<10).should == nil
+  end
+
+  it "returns value passed to break if interrupted by break" do
+    (break 123 while true).should == 123
+  end
+
+  it "returns nil if interrupted by break with no arguments" do
+    (break while true).should == nil
+  end
+
+  it "skips to end of body with next" do
+    i = 0
+    j = 0
+    ((i+=1) == 3 ? next : j+=i) while i <= 10
+    j.should == 63
+  end
+
+  # NATFIXME: Infinite loop
+  xit "restarts the current iteration without reevaluating condition with redo" do
+    i = 0
+    j = 0
+    (i+=1) == 4 ? redo : j+=i while (i+=1) <= 10
+    j.should == 34
+  end
+end
+
+describe "The while modifier with begin .. end block" do
+  it "runs block while the expression is true" do
+    i = 0
+    begin
+      i += 1
+    end while i < 3
+
+    i.should == 3
+  end
+
+  it "stops running block if interrupted by break" do
+    i = 0
+    begin
+      i += 1
+      break if i > 5
+    end while i < 10
+
+    i.should == 6
+  end
+
+  it "returns value passed to break if interrupted by break" do
+    (begin; break 123; end while true).should == 123
+  end
+
+  it "returns nil if interrupted by break with no arguments" do
+    (begin; break; end while true).should == nil
+  end
+
+  it "runs block at least once (even if the expression is false)" do
+    i = 0
+    begin
+      i += 1
+    end while false
+
+    i.should == 1
+  end
+
+  it "evaluates condition after block execution" do
+    a = []
+    i = 0
+    begin
+      a << i
+    end while (i+=1)<5
+    a.should == [0, 1, 2, 3, 4]
+  end
+
+  it "skips to end of body with next" do
+    a = []
+    i = 0
+    begin
+      next if i==3
+      a << i
+    end while (i+=1)<5
+    a.should == [0, 1, 2, 4]
+  end
+
+  # NATFIXME: Infinite loop
+  xit "restarts the current iteration without reevaluating condition with redo" do
+    a = []
+    i = 0
+    j = 0
+    begin
+      a << i
+      j+=1
+      redo if j<3
+    end while (i+=1)<3
+    a.should == [0, 0, 0, 1, 2]
+  end
+end