diff --git a/lib/repl_type_completor/result.rb b/lib/repl_type_completor/result.rb
index edfaa64..562e2d5 100644
--- a/lib/repl_type_completor/result.rb
+++ b/lib/repl_type_completor/result.rb
@@ -46,7 +46,7 @@ def completion_candidates
       in [:require_relative, name]
         RequirePaths.require_relative_completions(name, @source_file)
       in [:call_or_const, name, type, self_call]
-        ((self_call ? type.all_methods : type.methods).map(&:to_s) - HIDDEN_METHODS) | type.constants
+        ((self_call ? type.all_methods : type.methods).map(&:to_s) - HIDDEN_METHODS).sort | type.constants.sort
       in [:const, name, type, scope]
         if type
           scope_constants = type.types.flat_map do |t|
@@ -60,9 +60,9 @@ def completion_candidates
         ivars = scope.instance_variables.sort
         name == '@' ? ivars + scope.class_variables.sort : ivars
       in [:cvar, name, scope]
-        scope.class_variables
+        scope.class_variables.sort
       in [:gvar, name, scope]
-        scope.global_variables
+        scope.global_variables.sort
       in [:symbol, name]
         filter_symbol_candidates(Symbol.all_symbols, name, limit: 100)
       in [:aref, key_type, name, receiver_type]
@@ -70,18 +70,22 @@ def completion_candidates
         keys = receiver_type.types.grep(Types::InstanceType).select do |t|
           Hash == t.klass
         end.flat_map do |t|
-          t.instances.flat_map(&:keys).grep(key_type).uniq.sort
+          t.instances.flat_map(&:keys).grep(key_type).uniq
         end
         if key_type == Symbol
           keys = Symbol.all_symbols if keys.empty? && name.size >= 1
           filter_symbol_candidates(keys, name, limit: 100)
         else
-          keys.select { _1.start_with?(name) }.sort
+          keys.sort
         end
       in [:call, name, type, self_call]
-        (self_call ? type.all_methods : type.methods).map(&:to_s) - HIDDEN_METHODS
+        methods = (self_call ? type.all_methods : type.methods).map(&:to_s) - HIDDEN_METHODS
+        # Alphabetical order, but internal methods (leading underscore) last.
+        # `_1[0] == '_'` because `start_with?('_')` raises EncodingError if the
+        # method name's encoding is incompatible with US-ASCII.
+        methods.sort_by { [_1[0] == '_' ? 1 : 0, _1] }
       in [:lvar_or_method, name, scope]
-        scope.self_type.all_methods.map(&:to_s) | scope.local_variables | RESERVED_WORDS
+        scope.local_variables.sort | scope.self_type.all_methods.map(&:to_s).sort | RESERVED_WORDS
       else
         []
       end
diff --git a/test/repl_type_completor/test_repl_type_completor.rb b/test/repl_type_completor/test_repl_type_completor.rb
index 23d76fd..e689820 100644
--- a/test/repl_type_completor/test_repl_type_completor.rb
+++ b/test/repl_type_completor/test_repl_type_completor.rb
@@ -293,6 +293,43 @@ def with_failing_method(klass, method_name, message)
       klass.define_method(method_name, original_method)
     end
 
+    def test_call_candidates_are_sorted_with_underscore_methods_last
+      type = Struct.new(:methods).new(%i[_zeta beta _alpha alpha])
+      result = ReplTypeCompletor::Result.new([:call, '', type, false], binding, __FILE__)
+
+      assert_equal %w[alpha beta _alpha _zeta], result.completion_candidates
+    end
+
+    def test_call_or_const_candidates_are_sorted_within_groups
+      type = Struct.new(:methods, :constants).new(%i[z_method a_method], %i[ZConst AConst])
+      result = ReplTypeCompletor::Result.new([:call_or_const, '', type, false], binding, __FILE__)
+
+      assert_equal %w[a_method z_method AConst ZConst], result.completion_candidates
+    end
+
+    def test_const_candidates_are_sorted_before_reserved_words
+      scope = Struct.new(:constants).new(%w[ZConst AConst])
+      result = ReplTypeCompletor::Result.new([:const, '', nil, scope], binding, __FILE__)
+
+      assert_equal %w[AConst ZConst] + ReplTypeCompletor::Result::RESERVED_WORDS, result.completion_candidates
+    end
+
+    def test_ivar_candidates_are_sorted_within_groups
+      scope = Struct.new(:instance_variables, :class_variables).new(%w[@z @a], %w[@@z @@a])
+      result = ReplTypeCompletor::Result.new([:ivar, '@', scope], binding, __FILE__)
+
+      assert_equal %w[a z @a @z], result.completion_candidates
+    end
+
+    def test_lvar_or_method_candidates_are_sorted_within_groups
+      type = Struct.new(:all_methods).new(%i[z_method a_method])
+      scope = Struct.new(:self_type, :local_variables).new(type, %w[z_local a_local])
+      result = ReplTypeCompletor::Result.new([:lvar_or_method, '', scope], binding, __FILE__)
+
+      expected = %w[a_local z_local a_method z_method] + ReplTypeCompletor::Result::RESERVED_WORDS
+      assert_equal expected, result.completion_candidates
+    end
+
     def test_analyze_error
       with_failing_method(ReplTypeCompletor.singleton_class, :analyze_code, 'error_in_analyze_code') do
         assert_nil ReplTypeCompletor.analyze('1.', binding: binding)