diff --git a/lib/prism/orm/dirty.rb b/lib/prism/orm/dirty.rb
new file mode 100644
index 0000000..f405953
--- /dev/null
+++ b/lib/prism/orm/dirty.rb
@@ -0,0 +1,120 @@
+module Prism
+  module Orm
+    # ActiveModel::Dirty-lite: tracks unsaved attribute changes on a Model
+    # instance. Like Callbacks/Validatable, this is included as a plain
+    # module and invoked from explicit call sites in Model (Model#[]=,
+    # #load_row, #save) rather than overriding those methods itself -
+    # Model defines them directly in its own class body, which always
+    # wins method lookup over an included module, so overriding them here
+    # would silently do nothing.
+    module Dirty
+      # Attribute name => value it held before the current unsaved change.
+      # Frozen-ish read view; callers get a copy, not the internal hash.
+      def changed_attributes
+        (@changed_attributes ||= {}).each_with_object({}) { |(k, v), h| h[k] = humanize_dirty_value(k, v) }
+      end
+
+      def changed?
+        !(@changed_attributes ||= {}).empty?
+      end
+
+      def changed
+        (@changed_attributes ||= {}).keys
+      end
+
+      # { "title" => [old_value, current_value], ... }
+      def changes
+        (@changed_attributes ||= {}).each_with_object({}) do |(key, old_value), result|
+          result[key] = [humanize_dirty_value(key, old_value), humanize_dirty_value(key, @attributes[key])]
+        end
+      end
+
+      def attribute_changed?(name)
+        (@changed_attributes ||= {}).key?(name.to_s)
+      end
+
+      def attribute_was(name)
+        name = name.to_s
+        raw = attribute_changed?(name) ? @changed_attributes[name] : @attributes[name]
+        humanize_dirty_value(name, raw)
+      end
+
+      def attribute_change(name)
+        name = name.to_s
+        return nil unless attribute_changed?(name)
+        [humanize_dirty_value(name, @changed_attributes[name]), humanize_dirty_value(name, @attributes[name])]
+      end
+
+      # Reverts unsaved changes (all, or just the given attribute names)
+      # back to the value they held after the last load/save.
+      def restore_attributes(names = nil)
+        names = names ? names.map(&:to_s) : changed
+        names.each do |name|
+          next unless (@changed_attributes ||= {}).key?(name)
+          @attributes[name] = @changed_attributes.delete(name)
+        end
+        self
+      end
+
+      # Snapshot of what #changes held right after the most recent #save,
+      # matching Rails' saved_changes/previous_changes. Empty before the
+      # first save and while there are only unsaved (not-yet-persisted)
+      # changes - use #changes for those.
+      def saved_changes
+        (@saved_changes ||= {}).each_with_object({}) { |(k, v), h| h[k] = v.dup }
+      end
+
+      def saved_change_to_attribute?(name)
+        (@saved_changes ||= {}).key?(name.to_s)
+      end
+
+      def saved_change_to_attribute(name)
+        (@saved_changes ||= {})[name.to_s]
+      end
+
+      private
+
+      # An `encrypts`-backed attribute stores ciphertext in @attributes -
+      # track_attribute_change/#[]= only ever see the raw column value, so
+      # without this every dirty-tracking read (changes/attribute_was/...)
+      # would leak ciphertext bytes instead of the plaintext the model's
+      # own reader returns. Encryption is always included on Model (see
+      # Model's include list), so encrypted_attributes is always defined,
+      # just empty for a class with no `encrypts` at all - the common case
+      # skips straight past this and returns the raw value unchanged.
+      def humanize_dirty_value(name, raw_value)
+        return raw_value unless self.class.encrypted_attributes.key?(name.to_s)
+        Encryption.decrypt_with_rotation(self.class.encryption_key_for(name),
+                                          self.class.encryption_previous_keys_for(name),
+                                          raw_value)
+      end
+
+      # Called from Model#[]= on every write. A value written back to what
+      # it was before the current chain of unsaved changes started is not
+      # dirty anymore (matches ActiveModel: set then un-set == no change).
+      def track_attribute_change(key, old_value, new_value)
+        return if old_value == new_value
+        pending = (@changed_attributes ||= {})
+        if pending.key?(key)
+          pending.delete(key) if pending[key] == new_value
+        else
+          pending[key] = old_value
+        end
+      end
+
+      # Called right after a successful insert/update: today's unsaved
+      # changes become saved_changes, and the record is clean again.
+      def changes_applied
+        @saved_changes = changes
+        @changed_attributes = {}
+      end
+
+      # Called from Model#load_row (fresh load or #reload): no changes,
+      # nothing saved yet in this instance's lifetime.
+      def clear_changes_information
+        @changed_attributes = {}
+        @saved_changes = {}
+      end
+    end
+  end
+end