diff --git a/backend/alembic/versions/d9d57470c1f1_add_site_settings.py b/backend/alembic/versions/d9d57470c1f1_add_site_settings.py
new file mode 100644
index 0000000..ca8a821
--- /dev/null
+++ b/backend/alembic/versions/d9d57470c1f1_add_site_settings.py
@@ -0,0 +1,46 @@
+"""add site_settings
+
+Revision ID: d9d57470c1f1
+Revises: a33f7a001c32
+Create Date: 2026-10-22
+"""
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "d9d57470c1f1"
+down_revision: str | Sequence[str] | None = "a33f7a001c32"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table(
+        "site_settings",
+        sa.Column("key", sa.String(length=100), nullable=False),
+        sa.Column("value", postgresql.JSONB(astext_type=sa.Text()), nullable=False),
+        sa.Column("updated_by", sa.Uuid(), nullable=True),
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("now()"),
+            nullable=False,
+        ),
+        sa.ForeignKeyConstraint(["updated_by"], ["accounts.id"], ondelete="SET NULL"),
+        sa.PrimaryKeyConstraint("key"),
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_table("site_settings")
+    # ### end Alembic commands ###
diff --git a/backend/app/main.py b/backend/app/main.py
index 9b6e901..40e4f67 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -4,7 +4,7 @@
 from app.config import get_settings
 from app.errors import register_exception_handlers
 from app.logging import RequestLoggingMiddleware, configure_logging
-from app.routers import content, feedback, health
+from app.routers import content, feedback, health, settings
 
 configure_logging()
 
@@ -23,6 +23,7 @@
 app.add_middleware(RequestLoggingMiddleware)
 
 app.include_router(health.router, prefix="/api")
+app.include_router(settings.router, prefix="/api")
 
 app.include_router(content.router, prefix="/api")
 app.include_router(feedback.router, prefix="/api")
diff --git a/backend/app/models/__init__.py b/backend/app/models/__init__.py
index ed22494..776359a 100644
--- a/backend/app/models/__init__.py
+++ b/backend/app/models/__init__.py
@@ -15,6 +15,7 @@
     Texter,
 )
 from app.models.shift import Shift, ShiftEndReason
+from app.models.site_setting import SiteSetting
 
 __all__ = [
     "Account",
@@ -30,6 +31,7 @@
     "FeedbackSubmission",
     "Message",
     "MessageSender",
+    "SiteSetting",
     "Shift",
     "ShiftEndReason",
     "Texter",
diff --git a/backend/app/models/site_setting.py b/backend/app/models/site_setting.py
new file mode 100644
index 0000000..76cf624
--- /dev/null
+++ b/backend/app/models/site_setting.py
@@ -0,0 +1,24 @@
+import uuid
+from datetime import datetime
+from typing import Any
+
+from sqlalchemy import DateTime, ForeignKey, String, func
+from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.database import Base
+
+
+class SiteSetting(Base):
+    """Editable single values (TDD 4.5.3). Valid keys and types live in the SETTINGS registry."""
+
+    __tablename__ = "site_settings"
+
+    key: Mapped[str] = mapped_column(String(100), primary_key=True)
+    value: Mapped[Any] = mapped_column(JSONB)
+    updated_by: Mapped[uuid.UUID | None] = mapped_column(
+        ForeignKey("accounts.id", ondelete="SET NULL")
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )
diff --git a/backend/app/routers/settings.py b/backend/app/routers/settings.py
new file mode 100644
index 0000000..a2c1909
--- /dev/null
+++ b/backend/app/routers/settings.py
@@ -0,0 +1,16 @@
+from typing import Annotated
+
+from fastapi import APIRouter, Depends
+from sqlalchemy.orm import Session
+
+from app.database import get_db
+from app.schemas.settings import SiteSettingsDTO
+from app.services.site_settings import SETTINGS, get_setting
+
+router = APIRouter(prefix="/settings", tags=["settings"])
+
+
+@router.get("", response_model=SiteSettingsDTO)
+def read_settings(db: Annotated[Session, Depends(get_db)]) -> SiteSettingsDTO:
+    values = {key: get_setting(db, key) for key, d in SETTINGS.items() if d.public}
+    return SiteSettingsDTO(**values)
diff --git a/backend/app/schemas/settings.py b/backend/app/schemas/settings.py
new file mode 100644
index 0000000..d276803
--- /dev/null
+++ b/backend/app/schemas/settings.py
@@ -0,0 +1,12 @@
+from typing import Literal
+
+from pydantic import AnyHttpUrl, BaseModel
+
+
+class SiteSettingsDTO(BaseModel):
+    tagline: str
+    contact_email: str
+    instagram_handle: str
+    responder_form_url: AnyHttpUrl | None
+    sms_number: str | None
+    channels: list[Literal["web", "sms"]]
diff --git a/backend/app/seed.py b/backend/app/seed.py
index 8f25235..12278fb 100644
--- a/backend/app/seed.py
+++ b/backend/app/seed.py
@@ -20,6 +20,7 @@ def seed_dev() -> None:
     if get_settings().environment != "development":
         raise RuntimeError("seed-dev is only allowed in the development environment")
 
+    import app.services.site_settings  # noqa: F401 -- registers its seed function
     from app.database import SessionLocal
 
     with SessionLocal.begin() as session:
diff --git a/backend/app/services/site_settings.py b/backend/app/services/site_settings.py
new file mode 100644
index 0000000..9f81ce4
--- /dev/null
+++ b/backend/app/services/site_settings.py
@@ -0,0 +1,73 @@
+import uuid
+from copy import deepcopy
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Annotated, Any, Literal
+
+from pydantic import AnyHttpUrl, EmailStr, Field, TypeAdapter, ValidationError
+from sqlalchemy.orm import Session
+
+from app.models.site_setting import SiteSetting
+from app.seed import register
+
+
+@register
+def seed_site_settings(db: Session) -> None:
+    set_setting(db, "tagline", "Someone to talk to, by students for students.", None)
+    set_setting(db, "responder_form_url", "https://example.com/responder-form", None)
+
+
+@dataclass(frozen=True)
+class SettingDef:
+    adapter: TypeAdapter[Any]
+    default: Any
+    public: bool
+    description: str
+
+
+def _def(tp: Any, default: Any, description: str, *, public: bool = True) -> SettingDef:
+    return SettingDef(TypeAdapter(tp), default, public, description)
+
+
+SETTINGS: dict[str, SettingDef] = {
+    "tagline": _def(Annotated[str, Field(max_length=200)], "", "Short tagline on the home page."),
+    "contact_email": _def(EmailStr, "peer2peernc@unc.edu", "Public contact email."),
+    "instagram_handle": _def(str, "uncpeer2peer", "Instagram handle, without the @."),
+    "responder_form_url": _def(AnyHttpUrl | None, None, "Link to the responder application form."),
+    "sms_number": _def(str | None, None, "Text line number, if SMS is enabled."),
+    "channels": _def(list[Literal["web", "sms"]], ["web"], "Which channels the line accepts."),
+    "line_launch_at": _def(
+        datetime | None,
+        None,
+        "When the line launches. Served by the status endpoint, not here.",
+        public=False,
+    ),
+}
+
+
+def get_setting(db: Session, key: str) -> Any:
+    """Stored value if valid, otherwise the default. Unknown keys raise KeyError."""
+    definition = SETTINGS[key]
+    row = db.get(SiteSetting, key)
+    if row is None:
+        return deepcopy(definition.default)
+    try:
+        return definition.adapter.validate_python(row.value)
+    except ValidationError:
+        return deepcopy(definition.default)
+
+
+def set_setting(db: Session, key: str, value: Any, actor_id: uuid.UUID | None) -> Any:
+    """Validate and upsert. Raises pydantic ValidationError on bad values."""
+    definition = SETTINGS[key]
+    validated = definition.adapter.validate_python(value)
+    stored = definition.adapter.dump_python(validated, mode="json")
+
+    row = db.get(SiteSetting, key)
+    if row is None:
+        db.add(SiteSetting(key=key, value=stored, updated_by=actor_id))
+    else:
+        row.value = stored
+        row.updated_by = actor_id
+    db.flush()
+    return validated
diff --git a/backend/pyproject.toml b/backend/pyproject.toml
index 36fe268..dc41520 100644
--- a/backend/pyproject.toml
+++ b/backend/pyproject.toml
@@ -9,6 +9,7 @@ dependencies = [
   "psycopg[binary]>=3.3",
   "pwdlib[argon2]>=0.3.1",
   "pydantic-settings>=2.15",
+  "pydantic[email]>=2.13.5",
   "sqlalchemy>=2.1",
   "uvicorn[standard]>=0.54",
 ]
diff --git a/backend/tests/test_site_settings.py b/backend/tests/test_site_settings.py
new file mode 100644
index 0000000..6f62d32
--- /dev/null
+++ b/backend/tests/test_site_settings.py
@@ -0,0 +1,39 @@
+import pytest
+from fastapi.testclient import TestClient
+from pydantic import ValidationError
+from sqlalchemy.orm import Session
+
+from app.services.site_settings import get_setting, set_setting
+
+
+def test_defaults_when_nothing_stored(db: Session) -> None:
+    assert get_setting(db, "contact_email") == "peer2peernc@unc.edu"
+    assert get_setting(db, "channels") == ["web"]
+    assert get_setting(db, "responder_form_url") is None
+
+
+def test_stored_value_wins(db: Session) -> None:
+    set_setting(db, "tagline", "Talk to a peer", None)
+    assert get_setting(db, "tagline") == "Talk to a peer"
+
+
+def test_unknown_key_raises(db: Session) -> None:
+    with pytest.raises(KeyError):
+        get_setting(db, "nope")
+
+
+def test_set_rejects_bad_email(db: Session) -> None:
+    with pytest.raises(ValidationError):
+        set_setting(db, "contact_email", "not-an-email", None)
+
+
+def test_set_rejects_non_url(db: Session) -> None:
+    with pytest.raises(ValidationError):
+        set_setting(db, "responder_form_url", "not a url", None)
+
+
+def test_non_public_keys_not_served(db: Session, client: TestClient) -> None:
+    set_setting(db, "line_launch_at", "2026-11-01T00:00:00Z", None)
+    body = client.get("/api/settings").json()
+    assert "line_launch_at" not in body
+    assert body["contact_email"] == "peer2peernc@unc.edu"
diff --git a/backend/uv.lock b/backend/uv.lock
index 35077f9..84ccc79 100644
--- a/backend/uv.lock
+++ b/backend/uv.lock
@@ -396,6 +396,28 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/02/08/9c41fb51ab5b43eb21674aff13df270e8ba6c4b29c8624e328dc7a9482af/distlib-0.4.3-py2.py3-none-any.whl", hash = "sha256:4b0ce306c966eb73bc3a7b6abad017c556dadd92c44701562cd528ac7fde4d5b", size = 470628, upload-time = "2026-06-12T08:04:50.506Z" },
 ]
 
+[[package]]
+name = "dnspython"
+version = "2.9.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/ef/4a/50822184bd67cc6493f0fb6a880749158fcd31ab3fa07409acfd91f9fc85/dnspython-2.9.0.tar.gz", hash = "sha256:b44dc6b18f07a8b1c56676a19fbfdb5209415b046a9cece286baafa87ff3f7f1", size = 423560, upload-time = "2026-10-09T00:07:24.352Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/10/02/cdcc9b7c051786a103c3b09e1003a82fa0c66bcb91ffbdabcfbf7b4163b9/dnspython-2.9.0-py3-none-any.whl", hash = "sha256:9a4aedb833c3c1b49214d04d44d3032ab7a9135f7c1d29a549b4ff78fd82fda9", size = 354822, upload-time = "2026-10-09T00:07:22.622Z" },
+]
+
+[[package]]
+name = "email-validator"
+version = "2.3.0"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "dnspython" },
+    { name = "idna" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/f5/22/900cb125c76b7aaa450ce02fd727f452243f2e91a61af068b40adba60ea9/email_validator-2.3.0.tar.gz", hash = "sha256:9fc05c37f2f6cf439ff414f8fc46d917929974a82244c20eb10231ba60c54426", size = 51238, upload-time = "2025-08-26T13:09:06.831Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/de/15/545e2b6cf2e3be84bc1ed85613edd75b8aea69807a71c26f4ca6a9258e82/email_validator-2.3.0-py3-none-any.whl", hash = "sha256:80f13f623413e6b197ae73bb10bf4eb0908faf509ad8362c5edeb0be7fd450b4", size = 35604, upload-time = "2025-08-26T13:09:05.858Z" },
+]
+
 [[package]]
 name = "fastapi"
 version = "0.142.2"
@@ -730,6 +752,7 @@ dependencies = [
     { name = "fastapi" },
     { name = "psycopg", extra = ["binary"] },
     { name = "pwdlib", extra = ["argon2"] },
+    { name = "pydantic", extra = ["email"] },
     { name = "pydantic-settings" },
     { name = "sqlalchemy" },
     { name = "uvicorn", extra = ["standard"] },
@@ -752,6 +775,7 @@ requires-dist = [
     { name = "fastapi", specifier = ">=0.142" },
     { name = "psycopg", extras = ["binary"], specifier = ">=3.3" },
     { name = "pwdlib", extras = ["argon2"], specifier = ">=0.3.1" },
+    { name = "pydantic", extras = ["email"], specifier = ">=2.13.5" },
     { name = "pydantic-settings", specifier = ">=2.15" },
     { name = "sqlalchemy", specifier = ">=2.1" },
     { name = "uvicorn", extras = ["standard"], specifier = ">=0.54" },
@@ -885,6 +909,11 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/eb/47/c95ffc2009878c7aac0c5e08528022dcb885933252a88b5f170058014464/pydantic-2.13.5-py3-none-any.whl", hash = "sha256:346a034f080da3755d8e9cb5e00e8b07de1d39e4f6e2c87d8ab7cafa0b269a73", size = 472589, upload-time = "2026-08-28T14:03:59.136Z" },
 ]
 
+[package.optional-dependencies]
+email = [
+    { name = "email-validator" },
+]
+
 [[package]]
 name = "pydantic-core"
 version = "2.46.5"