diff --git a/CHANGELOG.md b/CHANGELOG.md
index d55ce40ac5b3..49d929c46ab5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## Current develop
 
 ### Added (new features/APIs/variables/...)
+- [[PR 907]](https://github.com/parthenon-hpc-lab/parthenon/pull/907) PEP1: Allow subclassing StateDescriptor
 - [[PR 932]](https://github.com/parthenon-hpc-lab/parthenon/pull/932) Add GetOrAddFlag to metadata
 - [[PR 931]](https://github.com/parthenon-hpc-lab/parthenon/pull/931) Allow SparsePacks with subsets of blocks
 - [[PR 921]](https://github.com/parthenon-hpc-lab/parthenon/pull/921) Add more flexible ways of adding and using MeshData/MeshBlockData objects to DataCollections
diff --git a/src/interface/packages.hpp b/src/interface/packages.hpp
index 285a815bf9ea..1ef6db59f58f 100644
--- a/src/interface/packages.hpp
+++ b/src/interface/packages.hpp
@@ -16,6 +16,7 @@
 
 #include <memory>
 #include <string>
+#include <vector>
 
 #include "basic_types.hpp"
 
@@ -26,15 +27,47 @@ class Packages_t {
   Packages_t() = default;
   void Add(const std::shared_ptr<StateDescriptor> &package);
 
-  std::shared_ptr<StateDescriptor> const &Get(const std::string &name) {
+  std::shared_ptr<StateDescriptor> const &Get(const std::string &name) const {
     return packages_.at(name);
   }
 
+  // Retrieve a package pointer, cast to a given type T
+  template <typename T>
+  T *Get(const std::string &name) const {
+    return static_cast<T *>(packages_.at(name).get());
+  }
+
   const Dictionary<std::shared_ptr<StateDescriptor>> &AllPackages() const {
     return packages_;
   }
   Dictionary<std::shared_ptr<StateDescriptor>> &AllPackages() { return packages_; }
 
+  // Returns a sub-Dictionary containing just pointers to packages of type T.
+  // Dictionary is a *new copy*, and members are bare pointers, not shared_ptr.
+  template <typename T>
+  const Dictionary<T *> AllPackagesOfType() const {
+    Dictionary<T *> sub_dict;
+    for (auto package : packages_) {
+      if (T *cast_package = dynamic_cast<T *>(package.second.get())) {
+        sub_dict[package.first] = cast_package;
+      }
+    }
+    return sub_dict;
+  }
+
+  // Returns a list of pointers to packages of type T.
+  // List contains bare pointers, not shared_ptr objects
+  template <typename T>
+  const std::vector<T *> ListPackagesOfType() const {
+    std::vector<T *> sub_list;
+    for (auto package : packages_) {
+      if (T *cast_package = dynamic_cast<T *>(package.second.get())) {
+        sub_list.append(cast_package);
+      }
+    }
+    return sub_list;
+  }
+
  private:
   Dictionary<std::shared_ptr<StateDescriptor>> packages_;
 };
diff --git a/src/interface/state_descriptor.hpp b/src/interface/state_descriptor.hpp
index ff21e628147c..5bb37ea83b60 100644
--- a/src/interface/state_descriptor.hpp
+++ b/src/interface/state_descriptor.hpp
@@ -108,6 +108,9 @@ class StateDescriptor {
     }
   }
 
+  // Virtual destructor for subclassing
+  virtual ~StateDescriptor() = default;
+
   static std::shared_ptr<StateDescriptor>
   CreateResolvedStateDescriptor(Packages_t &packages);
 
@@ -429,7 +432,7 @@ class StateDescriptor {
 
   friend std::ostream &operator<<(std::ostream &os, const StateDescriptor &sd);
 
- private:
+ protected:
   void InvertControllerMap();
 
   Params params_;