diff --git a/docs/operating_system_filtering.md b/docs/operating_system_filtering.md
new file mode 100644
index 0000000..6bb69f5
--- /dev/null
+++ b/docs/operating_system_filtering.md
@@ -0,0 +1,65 @@
+# **Understanding the OS Filtering Mechanism**
+
+## **Overview**
+This function filters devices based on their **reachability** and an optional **OS category filter**. It supports:
+
+- **Broad OS categories** (e.g., `"Linux"` includes all OS versions under `"Linux"`)
+- **Specific OS categories** (e.g., `"Debian"` only includes OS versions under `"Linux" -> "Debian"`)
+- **Single category selection** (Only `target_os="Linux"` OR `target_os="Debian"` is used, never both at once)
+
+---
+
+## **How It Works (Simplified)**
+
+### **1. OS Category Expansion**
+The function first expands the `target_os` category by retrieving all valid OS names under it.
+
+#### **Example OS Category Structure:**
+```json
+{
+    "Linux": {
+        "Debian": [
+            "Debian GNU/Linux 12 (bookworm)",
+            "Debian GNU/Linux 11 (bullseye)"
+        ],
+        "Ubuntu": [
+            "Ubuntu 24.04.1 LTS"
+        ]
+    }
+}
+```
+
+#### **Expanding Different `target_os` Values:**
+
+| `target_os`   | Expanded OS Versions |
+|--------------|---------------------------------------------------|
+| `"Linux"`   | `{ "Debian GNU/Linux 12 (bookworm)", "Debian GNU/Linux 11 (bullseye)", "Ubuntu 24.04.1 LTS" }` |
+| `"Debian"`  | `{ "Debian GNU/Linux 12 (bookworm)", "Debian GNU/Linux 11 (bullseye)" }` |
+
+---
+
+### **2. Device Filtering**
+Once the function has the allowed OS versions, it checks each device:
+
+#### **Example Device List:**
+```json
+[
+    {"device_id": "A1", "device_os": "Debian GNU/Linux 12 (bookworm)", "reachable": true},
+    {"device_id": "A2", "device_os": "Ubuntu 24.04.1 LTS", "reachable": true},
+    {"device_id": "A3", "device_os": "Windows 11", "reachable": true},
+    {"device_id": "A4", "device_os": "Debian GNU/Linux 11 (bullseye)", "reachable": false}
+]
+```
+
+#### **Filtering Behavior:**
+| Device ID | Device OS                         | Reachable | Matches `target_os="Linux"` | Matches `target_os="Debian"` |
+|-----------|----------------------------------|-----------|-------------------------------|-------------------------------|
+| A1        | Debian GNU/Linux 12 (bookworm)  | ✅        | ✅                             | ✅                             |
+| A2        | Ubuntu 24.04.1 LTS              | ✅        | ✅                             | ❌                             |
+| A3        | Windows 11                      | ✅        | ❌                             | ❌                             |
+| A4        | Debian GNU/Linux 11 (bullseye)  | ❌        | ❌ (Unreachable)               | ❌ (Unreachable)               |
+
+#### **Final Output:**
+- If `target_os="Linux"`: `["A1", "A2"]`
+- If `target_os="Debian"`: `["A1"]`
+- If `target_os=None`: `["A1", "A2", "A3"]` or `target_os` is undefined
\ No newline at end of file
diff --git a/examples/aggregate_example.yaml b/examples/aggregate_example.yaml
index b43ded5..ecf7648 100644
--- a/examples/aggregate_example.yaml
+++ b/examples/aggregate_example.yaml
@@ -1,7 +1,7 @@
 ---
 name: Echo some text in the terminal of the device
 group: "Development"
-target_os: "Debian"
+target_os: "Linux" # <----
 variables:
   - name: package_manager
     value: "apt"
diff --git a/meshbook.py b/meshbook.py
index 05a32ae..3f1bd52 100644
--- a/meshbook.py
+++ b/meshbook.py
@@ -96,22 +96,40 @@ async def compile_group_list(session: meshctrl.Session) -> dict:
     return local_device_list
 
 async def filter_targets(devices: list[dict], os_categories: dict, target_os: str = None) -> list[str]:
-    """Filters devices based on reachability and optional OS criteria."""
+    """Filters devices based on reachability and optional OS criteria, supporting nested OS categories."""
     valid_devices = []
 
+    def get_os_variants(category: str, os_map: dict) -> set:
+        """Extracts all OS names under a given category if it exists."""
+        for key, value in os_map.items():
+            if key == category:
+                if isinstance(value, dict):  # Expand nested categories
+                    os_set = set()
+                    for subcat in value:
+                        os_set.update(get_os_variants(subcat, value))
+                    return os_set
+                elif isinstance(value, list):  # Direct OS list
+                    return set(value)
+        return set()
+
+    allowed_os = set()
+
+    # Identify correct OS filtering scope
+    for key in os_categories:
+        if key == target_os:
+            allowed_os = get_os_variants(target_os, os_categories)
+            break  # Stop searching once a match is found
+
+        if isinstance(os_categories[key], dict) and target_os in os_categories[key]:
+            allowed_os = get_os_variants(target_os, os_categories[key])
+            break  # Stop searching once a match is found
+
     for device in devices:
         if not device["reachable"]:
             continue  # Skip unreachable devices.
 
-        match target_os:
-            case None:  # No filtering needed.
-                pass
-            case _ if target_os in os_categories and device["device_os"] in os_categories[target_os]:
-                pass  # Allowed OS, continue processing.
-            case _:  
-                continue  # Skip if the OS is not in the allowed category.
-
-        valid_devices.append(device["device_id"])
+        if not target_os or device["device_os"] in allowed_os:
+            valid_devices.append(device["device_id"])
 
     return valid_devices
 
diff --git a/os_categories.json b/os_categories.json
index 7346750..4eaefe9 100644
--- a/os_categories.json
+++ b/os_categories.json
@@ -1,9 +1,16 @@
 {
-    "Debian": [
-        "Debian GNU/Linux 12 (bookworm)",
-        "Debian GNU/Linux 11 (bullseye)"
-    ],
-    "Ubuntu": [
-        "Ubuntu 24.04.1 LTS"
-    ]
+    "Linux": {
+        "Debian": [
+            "Debian GNU/Linux 12 (bookworm)",
+            "Debian GNU/Linux 11 (bullseye)"
+        ],
+        "Ubuntu": [
+            "Ubuntu 24.04.1 LTS"
+        ]
+    },
+    "MacOS": {
+        "Sequoia": [
+            "macOS 15.0.1"
+        ]
+    }
 }
\ No newline at end of file