diff --git a/.gitignore b/.gitignore
index 7e14a5b..76f90e5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,4 +4,5 @@ __pycache__/
 .env
 .envrc
 .DS_Store
-ca-certificate.crt
\ No newline at end of file
+ca-certificate.crt
+firebase-service-account-key.json
\ No newline at end of file
diff --git a/app.py b/app.py
index 9720900..a1fa4df 100644
--- a/app.py
+++ b/app.py
@@ -23,6 +23,27 @@
 from src.utils.team_loader import TeamLoader
 from src.database import db
 
+import os
+import firebase_admin
+from firebase_admin import credentials, auth
+
+SERVICE_ACCOUNT_PATH = os.environ.get("GOOGLE_APPLICATION_CREDENTIALS")
+
+
+def initialize_firebase():
+    if not firebase_admin._apps:
+        if not SERVICE_ACCOUNT_PATH:
+            raise ValueError(
+                "GOOGLE_APPLICATION_CREDENTIALS is not set. Set it to your firebase-service-account-key.json path."
+            )
+        cred = credentials.Certificate(SERVICE_ACCOUNT_PATH)
+        firebase_admin.initialize_app(cred)
+        logging.info("Firebase app initialized.")
+    return firebase_admin.get_app()
+
+
+initialize_firebase()
+
 app = Flask(__name__)
 
 # CORS: allow frontend (different origin) to call this API
diff --git a/requirements.txt b/requirements.txt
index 6ef629f..fb220c9 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,3 +11,4 @@ Flask-APScheduler
 python-dotenv
 pytz
 gunicorn
+firebase-admin
\ No newline at end of file
diff --git a/src/mutations/login_user.py b/src/mutations/login_user.py
index b606738..b3bece6 100644
--- a/src/mutations/login_user.py
+++ b/src/mutations/login_user.py
@@ -1,19 +1,26 @@
 from graphql import GraphQLError
-from graphene import Mutation, String, Field
+from graphene import Mutation, String
 
+from firebase_admin import auth as firebase_auth
 from flask_jwt_extended import create_access_token, create_refresh_token
 from src.database import db
 
 
 class LoginUser(Mutation):
     class Arguments:
-        net_id = String(required=True, description="User's net ID (e.g. Cornell netid).")
+        id_token = String(required=True, description="Firebase ID token from the client.")
 
     access_token = String()
     refresh_token = String()
 
-    def mutate(self, info, net_id):
-        user = db["users"].find_one({"net_id": net_id})
+    def mutate(self, info, id_token):
+        try:
+            decoded = firebase_auth.verify_id_token(id_token)
+        except Exception:
+            raise GraphQLError("Invalid or expired token.")
+
+        firebase_uid = decoded["uid"]
+        user = db["users"].find_one({"firebase_uid": firebase_uid})
         if not user:
             raise GraphQLError("User not found.")
         identity = str(user["_id"])
diff --git a/src/mutations/signup_user.py b/src/mutations/signup_user.py
index eb6f6ae..4ff60b6 100644
--- a/src/mutations/signup_user.py
+++ b/src/mutations/signup_user.py
@@ -1,30 +1,38 @@
 from graphql import GraphQLError
 from graphene import Mutation, String
 
+from firebase_admin import auth as firebase_auth
 from flask_jwt_extended import create_access_token, create_refresh_token
 from src.database import db
 
 
 class SignupUser(Mutation):
     class Arguments:
-        net_id = String(required=True, description="User's net ID (e.g. Cornell netid).")
+        id_token = String(required=True, description="Firebase ID token from the client.")
         name = String(required=False, description="Display name.")
-        email = String(required=False, description="Email address.")
+        email = String(required=False, description="Email (overrides token email if provided).")
 
     access_token = String()
     refresh_token = String()
 
-    def mutate(self, info, net_id, name=None, email=None):
-        if db["users"].find_one({"net_id": net_id}):
-            raise GraphQLError("Net ID already exists.")
+    def mutate(self, info, id_token, name=None, email=None):
+        try:
+            decoded = firebase_auth.verify_id_token(id_token)
+        except Exception:
+            raise GraphQLError("Invalid or expired token.")
+
+        firebase_uid = decoded["uid"]
+        if db["users"].find_one({"firebase_uid": firebase_uid}):
+            raise GraphQLError("User already exists.")
+
+        email = email or decoded.get("email")
         user_doc = {
-            "net_id": net_id,
+            "firebase_uid": firebase_uid,
+            "email": email,
             "favorite_game_ids": [],
         }
         if name is not None:
             user_doc["name"] = name
-        if email is not None:
-            user_doc["email"] = email
         result = db["users"].insert_one(user_doc)
         identity = str(result.inserted_id)
         return SignupUser(
diff --git a/src/schema.py b/src/schema.py
index 70b5473..3bda2d0 100644
--- a/src/schema.py
+++ b/src/schema.py
@@ -31,9 +31,11 @@ class Mutation(ObjectType):
     create_team = CreateTeam.Field(description="Creates a new team.")
     create_youtube_video = CreateYoutubeVideo.Field(description="Creates a new youtube video.")
     create_article = CreateArticle.Field(description="Creates a new article.")
-    login_user = LoginUser.Field(description="Login by net_id; returns access_token and refresh_token.")
+    login_user = LoginUser.Field(
+        description="Login with Firebase ID token; returns access_token and refresh_token.",
+    )
     signup_user = SignupUser.Field(
-        description="Create a new user by net_id; returns access_token and refresh_token (no separate login needed).",
+        description="Create a new user with Firebase ID token; returns access_token and refresh_token.",
     )
     refresh_access_token = RefreshAccessToken.Field(
         description="Exchange a valid refresh token (in Authorization header) for a new access_token.",