diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9c34e040..8e2058db 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- The `specify-groups` option supports reading from STDIN when set to `-`
+
 ### Breaking Changes
 
 ### Added
diff --git a/Readme.md b/Readme.md
index 9c6480ca..1943f8f7 100644
--- a/Readme.md
+++ b/Readme.md
@@ -258,7 +258,8 @@ Options are:
         --failure-exit-code INT      Specify the exit code to use when tests fail
         --specify-groups SPECS       Use 'specify-groups' if you want to specify multiple specs running in multiple
                                      processes in a specific formation. Commas indicate specs in the same process,
-                                     pipes indicate specs in a new process. Cannot use with --single, --isolate, or
+                                     pipes indicate specs in a new process. If SPECS is a `-` the value for this
+                                     option is read from STDIN instead. Cannot use with --single, --isolate, or
                                      --isolate-n.  Ex.
                                      $ parallel_tests -n 3 . --specify-groups '1_spec.rb,2_spec.rb|3_spec.rb'
                                        Process 1 will contain 1_spec.rb and 2_spec.rb
diff --git a/lib/parallel_tests/cli.rb b/lib/parallel_tests/cli.rb
index 56b51dbc..7bebffcd 100644
--- a/lib/parallel_tests/cli.rb
+++ b/lib/parallel_tests/cli.rb
@@ -254,7 +254,8 @@ def parse_options!(argv)
           <<~TEXT.rstrip.split("\n").join("\n#{newline_padding}")
             Use 'specify-groups' if you want to specify multiple specs running in multiple
             processes in a specific formation. Commas indicate specs in the same process,
-            pipes indicate specs in a new process. Cannot use with --single, --isolate, or
+            pipes indicate specs in a new process. If SPECS is a '-' the value for this
+            option is read from STDIN instead. Cannot use with --single, --isolate, or
             --isolate-n.  Ex.
             $ parallel_tests -n 3 . --specify-groups '1_spec.rb,2_spec.rb|3_spec.rb'
               Process 1 will contain 1_spec.rb and 2_spec.rb
diff --git a/lib/parallel_tests/grouper.rb b/lib/parallel_tests/grouper.rb
index 44402764..b444a5e6 100644
--- a/lib/parallel_tests/grouper.rb
+++ b/lib/parallel_tests/grouper.rb
@@ -48,8 +48,15 @@ def in_even_groups_by_size(items, num_groups, options = {})
 
       private
 
+      def specified_groups(options)
+        groups = options[:specify_groups]
+        return groups if groups != '-'
+
+        $stdin.read.chomp
+      end
+
       def specify_groups(items, num_groups, options, groups)
-        specify_test_process_groups = options[:specify_groups].split('|')
+        specify_test_process_groups = specified_groups(options).split('|')
         if specify_test_process_groups.count > num_groups
           raise 'Number of processes separated by pipe must be less than or equal to the total number of processes'
         end
diff --git a/spec/parallel_tests/grouper_spec.rb b/spec/parallel_tests/grouper_spec.rb
index 57f0764c..0240c066 100644
--- a/spec/parallel_tests/grouper_spec.rb
+++ b/spec/parallel_tests/grouper_spec.rb
@@ -76,50 +76,116 @@ def call(num_groups, options = {})
       )
     end
 
-    it "groups specify_groups as specified when specify_groups is just one spec" do
-      expect(call(3, specify_groups: '1')).to eq([["1"], ["2", "5"], ["3", "4"]])
-    end
+    context 'with specific groups provided directly' do
+      it "groups specify_groups as specified when specify_groups is just one spec" do
+        expect(call(3, specify_groups: '1')).to eq([["1"], ["2", "5"], ["3", "4"]])
+      end
 
-    it "groups specify_groups as specified when specify_groups is just multiple specs in one process" do
-      expect(call(3, specify_groups: '3,1')).to eq([["3", "1"], ["5"], ["2", "4"]])
-    end
+      it "groups specify_groups as specified when specify_groups is just multiple specs in one process" do
+        expect(call(3, specify_groups: '3,1')).to eq([["3", "1"], ["5"], ["2", "4"]])
+      end
 
-    it "groups specify_groups as specified when specify_groups is multiple specs" do
-      expect(call(3, specify_groups: '1,2|4')).to eq([["1", "2"], ["4"], ["3", "5"]])
-    end
+      it "groups specify_groups as specified when specify_groups is multiple specs" do
+        expect(call(3, specify_groups: '1,2|4')).to eq([["1", "2"], ["4"], ["3", "5"]])
+      end
 
-    it "specify_groups aborts when number of specs separated by pipe is out of bounds" do
-      expect do
-        call(3, specify_groups: '1|2|3|4')
-      end.to raise_error(
-        "Number of processes separated by pipe must be less than or equal to the total number of processes"
-      )
-    end
+      it "specify_groups aborts when number of specs separated by pipe is out of bounds" do
+        expect do
+          call(3, specify_groups: '1|2|3|4')
+        end.to raise_error(
+          "Number of processes separated by pipe must be less than or equal to the total number of processes"
+        )
+      end
 
-    it "specify_groups aborts when spec passed in doesn't match existing specs" do
-      expect do
-        call(3, specify_groups: '1|2|6')
-      end.to raise_error(
-        "Could not find [\"6\"] from --specify-groups in the selected files & folders"
-      )
-    end
+      it "specify_groups aborts when spec passed in doesn't match existing specs" do
+        expect do
+          call(3, specify_groups: '1|2|6')
+        end.to raise_error(
+          "Could not find [\"6\"] from --specify-groups in the selected files & folders"
+        )
+      end
 
-    it "specify_groups aborts when spec passed in doesn't match existing specs again" do
-      expect do
-        call(3, specify_groups: '1,6|2')
-      end.to raise_error(
-        "Could not find [\"6\"] from --specify-groups in the selected files & folders"
-      )
-    end
+      it "specify_groups aborts when spec passed in doesn't match existing specs again" do
+        expect do
+          call(3, specify_groups: '1,6|2')
+        end.to raise_error(
+          "Could not find [\"6\"] from --specify-groups in the selected files & folders"
+        )
+      end
 
-    it "specify_groups aborts when number of specs is equal to number passed in" do
-      expect do
-        call(3, specify_groups: '1|2|3')
-      end.to raise_error(/The specs that aren't run:\n\["4", "5"\]/)
+      it "specify_groups aborts when number of specs is equal to number passed in" do
+        expect do
+          call(3, specify_groups: '1|2|3')
+        end.to raise_error(/The specs that aren't run:\n\["4", "5"\]/)
+      end
+
+      it "specify_groups does not abort when the every single spec is specified in it" do
+        expect(call(3, specify_groups: '1,2|3,4|5')).to eq([["1", "2"], ["3", "4"], ["5"]])
+      end
     end
 
-    it "specify_groups does not abort when the every single spec is specified in it" do
-      expect(call(3, specify_groups: '1,2|3,4|5')).to eq([["1", "2"], ["3", "4"], ["5"]])
+    context 'with specific groups provided through STDIN' do
+      it "groups specify_groups as specified when specify_groups is just one spec" do
+        allow($stdin).to receive(:read).and_return("1\n")
+
+        expect(call(3, specify_groups: '-')).to eq([["1"], ["2", "5"], ["3", "4"]])
+      end
+
+      it "groups specify_groups as specified when specify_groups is just multiple specs in one process" do
+        allow($stdin).to receive(:read).and_return("3,1\n")
+
+        expect(call(3, specify_groups: '-')).to eq([["3", "1"], ["5"], ["2", "4"]])
+      end
+
+      it "groups specify_groups as specified when specify_groups is multiple specs" do
+        allow($stdin).to receive(:read).and_return("1,2|4\n")
+
+        expect(call(3, specify_groups: '-')).to eq([["1", "2"], ["4"], ["3", "5"]])
+      end
+
+      it "specify_groups aborts when number of specs separated by pipe is out of bounds" do
+        allow($stdin).to receive(:read).and_return("1|2|3|4\n")
+
+        expect do
+          call(3, specify_groups: '-')
+        end.to raise_error(
+          "Number of processes separated by pipe must be less than or equal to the total number of processes"
+        )
+      end
+
+      it "specify_groups aborts when spec passed in doesn't match existing specs" do
+        allow($stdin).to receive(:read).and_return("1|2|6\n")
+
+        expect do
+          call(3, specify_groups: '-')
+        end.to raise_error(
+          "Could not find [\"6\"] from --specify-groups in the selected files & folders"
+        )
+      end
+
+      it "specify_groups aborts when spec passed in doesn't match existing specs again" do
+        allow($stdin).to receive(:read).and_return("1,6|2\n")
+
+        expect do
+          call(3, specify_groups: '-')
+        end.to raise_error(
+          "Could not find [\"6\"] from --specify-groups in the selected files & folders"
+        )
+      end
+
+      it "specify_groups aborts when number of specs is equal to number passed in" do
+        allow($stdin).to receive(:read).and_return("1|2|3\n")
+
+        expect do
+          call(3, specify_groups: '-')
+        end.to raise_error(/The specs that aren't run:\n\["4", "5"\]/)
+      end
+
+      it "specify_groups does not abort when the every single spec is specified in it" do
+        allow($stdin).to receive(:read).and_return("1,2|3,4|5\n")
+
+        expect(call(3, specify_groups: '-')).to eq([["1", "2"], ["3", "4"], ["5"]])
+      end
     end
   end