diff --git a/backend/models.py b/backend/models.py
index e0ad83c..dcdb537 100644
--- a/backend/models.py
+++ b/backend/models.py
@@ -27,6 +27,16 @@ class Permission(str, PyEnum):
     # Invite permissions
     MANAGE_INVITES = "manage_invites"
     VIEW_OWN_INVITES = "view_own_invites"
+    
+    # Booking permissions (regular users)
+    BOOK_APPOINTMENT = "book_appointment"
+    VIEW_OWN_APPOINTMENTS = "view_own_appointments"
+    CANCEL_OWN_APPOINTMENT = "cancel_own_appointment"
+    
+    # Availability/Appointments permissions (admin)
+    MANAGE_AVAILABILITY = "manage_availability"
+    VIEW_ALL_APPOINTMENTS = "view_all_appointments"
+    CANCEL_ANY_APPOINTMENT = "cancel_any_appointment"
 
 
 class InviteStatus(str, PyEnum):
@@ -36,6 +46,13 @@ class InviteStatus(str, PyEnum):
     REVOKED = "revoked"
 
 
+class AppointmentStatus(str, PyEnum):
+    """Status of an appointment."""
+    BOOKED = "booked"
+    CANCELLED_BY_USER = "cancelled_by_user"
+    CANCELLED_BY_ADMIN = "cancelled_by_admin"
+
+
 # Role name constants
 ROLE_ADMIN = "admin"
 ROLE_REGULAR = "regular"
@@ -43,19 +60,25 @@ ROLE_REGULAR = "regular"
 # Role definitions with their permissions
 ROLE_DEFINITIONS: dict[str, RoleConfig] = {
     ROLE_ADMIN: {
-        "description": "Administrator with audit and invite management access",
+        "description": "Administrator with audit, invite, and appointment management access",
         "permissions": [
             Permission.VIEW_AUDIT,
             Permission.MANAGE_INVITES,
+            Permission.MANAGE_AVAILABILITY,
+            Permission.VIEW_ALL_APPOINTMENTS,
+            Permission.CANCEL_ANY_APPOINTMENT,
         ],
     },
     ROLE_REGULAR: {
-        "description": "Regular user with counter, sum, and invite access",
+        "description": "Regular user with counter, sum, invite, and booking access",
         "permissions": [
             Permission.VIEW_COUNTER,
             Permission.INCREMENT_COUNTER,
             Permission.USE_SUM,
             Permission.VIEW_OWN_INVITES,
+            Permission.BOOK_APPOINTMENT,
+            Permission.VIEW_OWN_APPOINTMENTS,
+            Permission.CANCEL_OWN_APPOINTMENT,
         ],
     },
 }
diff --git a/backend/validate_constants.py b/backend/validate_constants.py
index b645114..e485399 100644
--- a/backend/validate_constants.py
+++ b/backend/validate_constants.py
@@ -2,7 +2,7 @@
 import json
 from pathlib import Path
 
-from models import ROLE_ADMIN, ROLE_REGULAR, InviteStatus
+from models import ROLE_ADMIN, ROLE_REGULAR, InviteStatus, AppointmentStatus
 
 
 def validate_shared_constants() -> None:
@@ -27,13 +27,28 @@ def validate_shared_constants() -> None:
         )
     
     # Validate invite statuses
-    expected_statuses = {s.name: s.value for s in InviteStatus}
-    if constants.get("inviteStatuses") != expected_statuses:
+    expected_invite_statuses = {s.name: s.value for s in InviteStatus}
+    if constants.get("inviteStatuses") != expected_invite_statuses:
         raise ValueError(
             f"Invite status mismatch in shared/constants.json. "
-            f"Expected: {expected_statuses}, Got: {constants.get('inviteStatuses')}"
+            f"Expected: {expected_invite_statuses}, Got: {constants.get('inviteStatuses')}"
         )
     
+    # Validate appointment statuses
+    expected_appointment_statuses = {s.name: s.value for s in AppointmentStatus}
+    if constants.get("appointmentStatuses") != expected_appointment_statuses:
+        raise ValueError(
+            f"Appointment status mismatch in shared/constants.json. "
+            f"Expected: {expected_appointment_statuses}, Got: {constants.get('appointmentStatuses')}"
+        )
+    
+    # Validate booking constants exist with required fields
+    booking = constants.get("booking", {})
+    required_booking_fields = ["slotDurationMinutes", "maxAdvanceDays", "minAdvanceDays", "noteMaxLength"]
+    for field in required_booking_fields:
+        if field not in booking:
+            raise ValueError(f"Missing booking constant '{field}' in shared/constants.json")
+    
     # Validate validation rules exist (structure check only)
     validation = constants.get("validation", {})
     required_fields = ["telegram", "signal", "nostrNpub"]
diff --git a/shared/constants.json b/shared/constants.json
index 0e278cc..54f1086 100644
--- a/shared/constants.json
+++ b/shared/constants.json
@@ -8,6 +8,17 @@
     "SPENT": "spent",
     "REVOKED": "revoked"
   },
+  "appointmentStatuses": {
+    "BOOKED": "booked",
+    "CANCELLED_BY_USER": "cancelled_by_user",
+    "CANCELLED_BY_ADMIN": "cancelled_by_admin"
+  },
+  "booking": {
+    "slotDurationMinutes": 15,
+    "maxAdvanceDays": 30,
+    "minAdvanceDays": 1,
+    "noteMaxLength": 144
+  },
   "validation": {
     "telegram": {
       "maxLengthAfterAt": 32,