diff --git a/bincio/segments/__init__.py b/bincio/segments/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/bincio/segments/models.py b/bincio/segments/models.py
new file mode 100644
index 0000000..c96da65
--- /dev/null
+++ b/bincio/segments/models.py
@@ -0,0 +1,29 @@
+"""Segment and SegmentEffort data models."""
+
+from dataclasses import dataclass, field
+from datetime import datetime
+from typing import Optional
+
+
+@dataclass
+class Segment:
+    id: str
+    name: str
+    polyline: list[list[float]]     # [[lat, lon], ...]
+    distance_m: float
+    bbox: list[float]               # [lon_min, lat_min, lon_max, lat_max]
+    created_by: str
+    created_at: datetime
+    sport: Optional[str] = None     # None = any sport
+
+
+@dataclass
+class SegmentEffort:
+    activity_id: str
+    started_at: datetime
+    elapsed_s: int
+    detected_at: datetime
+    avg_speed_kmh: Optional[float] = None
+    avg_hr_bpm: Optional[int] = None
+    avg_power_w: Optional[int] = None
+    np_power_w: Optional[int] = None
diff --git a/bincio/segments/store.py b/bincio/segments/store.py
new file mode 100644
index 0000000..e9d89fe
--- /dev/null
+++ b/bincio/segments/store.py
@@ -0,0 +1,181 @@
+"""Read/write segments and segment efforts to/from /var/bincio."""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import re
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Optional
+
+from bincio.segments.models import Segment, SegmentEffort
+
+# /var/bincio/segments/{id}.json
+_SEGMENTS_DIR = "segments"
+# /var/bincio/data/{handle}/segment_efforts/{segment_id}.json
+_EFFORTS_SUBDIR = "segment_efforts"
+
+
+# ── helpers ───────────────────────────────────────────────────────────────────
+
+def _segments_dir(data_dir: Path) -> Path:
+    d = data_dir / _SEGMENTS_DIR
+    d.mkdir(parents=True, exist_ok=True)
+    return d
+
+
+def _efforts_dir(data_dir: Path, handle: str) -> Path:
+    d = data_dir / handle / _EFFORTS_SUBDIR
+    d.mkdir(parents=True, exist_ok=True)
+    return d
+
+
+def _slugify(name: str) -> str:
+    s = name.lower().strip()
+    s = re.sub(r"[^a-z0-9]+", "-", s)
+    return s.strip("-")[:48]
+
+
+def _make_id(name: str) -> str:
+    slug = _slugify(name)
+    suffix = hashlib.sha256(name.encode()).hexdigest()[:4]
+    return f"{slug}-{suffix}"
+
+
+def _dt(s: str) -> datetime:
+    return datetime.fromisoformat(s.replace("Z", "+00:00"))
+
+
+def _iso(dt: datetime) -> str:
+    return dt.astimezone(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
+
+
+# ── serialisation ─────────────────────────────────────────────────────────────
+
+def _segment_to_dict(seg: Segment) -> dict:
+    return {
+        "id":          seg.id,
+        "name":        seg.name,
+        "sport":       seg.sport,
+        "polyline":    seg.polyline,
+        "distance_m":  round(seg.distance_m, 1),
+        "bbox":        [round(v, 6) for v in seg.bbox],
+        "created_by":  seg.created_by,
+        "created_at":  _iso(seg.created_at),
+    }
+
+
+def _segment_from_dict(d: dict) -> Segment:
+    return Segment(
+        id=d["id"],
+        name=d["name"],
+        sport=d.get("sport"),
+        polyline=d["polyline"],
+        distance_m=float(d["distance_m"]),
+        bbox=d["bbox"],
+        created_by=d["created_by"],
+        created_at=_dt(d["created_at"]),
+    )
+
+
+def _effort_to_dict(e: SegmentEffort) -> dict:
+    return {
+        "activity_id":   e.activity_id,
+        "started_at":    _iso(e.started_at),
+        "elapsed_s":     e.elapsed_s,
+        "avg_speed_kmh": e.avg_speed_kmh,
+        "avg_hr_bpm":    e.avg_hr_bpm,
+        "avg_power_w":   e.avg_power_w,
+        "np_power_w":    e.np_power_w,
+        "detected_at":   _iso(e.detected_at),
+    }
+
+
+def _effort_from_dict(d: dict) -> SegmentEffort:
+    return SegmentEffort(
+        activity_id=d["activity_id"],
+        started_at=_dt(d["started_at"]),
+        elapsed_s=int(d["elapsed_s"]),
+        avg_speed_kmh=d.get("avg_speed_kmh"),
+        avg_hr_bpm=d.get("avg_hr_bpm"),
+        avg_power_w=d.get("avg_power_w"),
+        np_power_w=d.get("np_power_w"),
+        detected_at=_dt(d["detected_at"]),
+    )
+
+
+# ── public API ────────────────────────────────────────────────────────────────
+
+def make_segment_id(name: str) -> str:
+    return _make_id(name)
+
+
+def save_segment(data_dir: Path, seg: Segment) -> None:
+    path = _segments_dir(data_dir) / f"{seg.id}.json"
+    path.write_text(json.dumps(_segment_to_dict(seg), ensure_ascii=False, indent=2), encoding="utf-8")
+
+
+def load_segment(data_dir: Path, segment_id: str) -> Optional[Segment]:
+    path = _segments_dir(data_dir) / f"{segment_id}.json"
+    if not path.exists():
+        return None
+    return _segment_from_dict(json.loads(path.read_text(encoding="utf-8")))
+
+
+def delete_segment(data_dir: Path, segment_id: str) -> bool:
+    path = _segments_dir(data_dir) / f"{segment_id}.json"
+    if not path.exists():
+        return False
+    path.unlink()
+    return True
+
+
+def list_segments(data_dir: Path, bbox: Optional[list[float]] = None) -> list[Segment]:
+    """Return all segments, optionally filtered to those overlapping bbox.
+
+    bbox = [lon_min, lat_min, lon_max, lat_max]
+    """
+    segs = []
+    for path in sorted(_segments_dir(data_dir).glob("*.json")):
+        try:
+            seg = _segment_from_dict(json.loads(path.read_text(encoding="utf-8")))
+        except Exception:
+            continue
+        if bbox is not None and not _bboxes_overlap(seg.bbox, bbox):
+            continue
+        segs.append(seg)
+    return segs
+
+
+def _bboxes_overlap(a: list[float], b: list[float]) -> bool:
+    """True if two [lon_min, lat_min, lon_max, lat_max] boxes overlap."""
+    return not (a[2] < b[0] or b[2] < a[0] or a[3] < b[1] or b[3] < a[1])
+
+
+# ── efforts ───────────────────────────────────────────────────────────────────
+
+def load_efforts(data_dir: Path, handle: str, segment_id: str) -> list[SegmentEffort]:
+    path = _efforts_dir(data_dir, handle) / f"{segment_id}.json"
+    if not path.exists():
+        return []
+    try:
+        return [_effort_from_dict(d) for d in json.loads(path.read_text(encoding="utf-8"))]
+    except Exception:
+        return []
+
+
+def save_efforts(data_dir: Path, handle: str, segment_id: str, efforts: list[SegmentEffort]) -> None:
+    path = _efforts_dir(data_dir, handle) / f"{segment_id}.json"
+    data = [_effort_to_dict(e) for e in efforts]
+    path.write_text(json.dumps(data, ensure_ascii=False, indent=2), encoding="utf-8")
+
+
+def add_effort(data_dir: Path, handle: str, segment_id: str, effort: SegmentEffort) -> None:
+    """Append an effort, replacing any existing effort for the same activity."""
+    efforts = load_efforts(data_dir, handle, segment_id)
+    efforts = [e for e in efforts if e.activity_id != effort.activity_id or
+               e.started_at != effort.started_at]
+    efforts.append(effort)
+    efforts.sort(key=lambda e: e.started_at, reverse=True)
+    save_efforts(data_dir, handle, segment_id, efforts)
diff --git a/bincio/serve/server.py b/bincio/serve/server.py
index 3ed5335..ab2903d 100644
--- a/bincio/serve/server.py
+++ b/bincio/serve/server.py
@@ -120,6 +120,13 @@ class GenericResponse(BaseModel):
     ok: bool = Field(True, description="Success flag")
 
 
+class CreateSegmentRequest(BaseModel):
+    name: str = Field(..., description="Segment name")
+    sport: Optional[str] = Field(default=None, description="Sport filter (e.g. cycling)")
+    polyline: list[list[float]] = Field(..., description="[[lat, lon], ...] ordered GPS points")
+    distance_m: float = Field(..., description="Segment length in metres")
+
+
 # ── Active job tracker ───────────────────────────────────────────────────────
 # Tracks in-progress upload/processing jobs so admins can see what's running.
 # Jobs are added when a streaming upload starts and removed when it finishes.
@@ -235,6 +242,8 @@ app.add_middleware(
 
 _VALID_HANDLE = re.compile(r'^[a-z0-9][a-z0-9_-]{0,29}$')
 from bincio.edit.ops import VALID_ACTIVITY_ID as _VALID_ACTIVITY_ID
+from bincio.segments import models as _seg_models
+from bincio.segments import store as _seg_store
 _SESSION_COOKIE  = "bincio_session"
 _COOKIE_MAX_AGE  = 30 * 86400  # 30 days
 _SESSION_DOMAIN  = os.environ.get("SESSION_DOMAIN") or None  # e.g. ".bincio.org" in production
@@ -2397,6 +2406,84 @@ async def upload_strava_zip(
     )
 
 
+# ── Segments ──────────────────────────────────────────────────────────────────
+
+@app.get("/api/segments")
+async def get_segments(
+    bbox: Optional[str] = None,
+    bincio_session: Optional[str] = Cookie(default=None),
+) -> JSONResponse:
+    """List segments, optionally filtered to a map viewport bbox (lon_min,lat_min,lon_max,lat_max)."""
+    _require_user(bincio_session)
+    parsed_bbox: Optional[list[float]] = None
+    if bbox:
+        try:
+            parts = [float(x) for x in bbox.split(",")]
+            if len(parts) == 4:
+                parsed_bbox = parts
+        except ValueError:
+            raise HTTPException(400, "bbox must be four comma-separated floats")
+    dd = _get_data_dir()
+    segs = _seg_store.list_segments(dd, parsed_bbox)
+    return JSONResponse([{
+        "id":         s.id,
+        "name":       s.name,
+        "sport":      s.sport,
+        "distance_m": s.distance_m,
+        "bbox":       s.bbox,
+        "polyline":   s.polyline,
+        "created_by": s.created_by,
+        "created_at": _seg_store._iso(s.created_at),
+    } for s in segs])
+
+
+@app.post("/api/segments")
+async def create_segment(
+    body: CreateSegmentRequest,
+    bincio_session: Optional[str] = Cookie(default=None),
+) -> JSONResponse:
+    user = _require_user(bincio_session)
+    if len(body.polyline) < 2:
+        raise HTTPException(400, "polyline must have at least 2 points")
+    if body.distance_m <= 0:
+        raise HTTPException(400, "distance_m must be positive")
+
+    lats = [p[0] for p in body.polyline]
+    lons = [p[1] for p in body.polyline]
+    bbox = [min(lons), min(lats), max(lons), max(lats)]
+
+    seg_id = _seg_store.make_segment_id(body.name)
+    from datetime import datetime, timezone as _tz
+    seg = _seg_models.Segment(
+        id=seg_id,
+        name=body.name,
+        sport=body.sport or None,
+        polyline=body.polyline,
+        distance_m=body.distance_m,
+        bbox=bbox,
+        created_by=user.handle,
+        created_at=datetime.now(_tz.utc),
+    )
+    _seg_store.save_segment(_get_data_dir(), seg)
+    return JSONResponse({"id": seg_id}, status_code=201)
+
+
+@app.delete("/api/segments/{segment_id}")
+async def delete_segment(
+    segment_id: str,
+    bincio_session: Optional[str] = Cookie(default=None),
+) -> JSONResponse:
+    user = _require_user(bincio_session)
+    dd = _get_data_dir()
+    seg = _seg_store.load_segment(dd, segment_id)
+    if seg is None:
+        raise HTTPException(404, "Segment not found")
+    if seg.created_by != user.handle and not user.is_admin:
+        raise HTTPException(403, "Not allowed")
+    _seg_store.delete_segment(dd, segment_id)
+    return JSONResponse({"ok": True})
+
+
 # ── Feedback ──────────────────────────────────────────────────────────────────
 
 _FEEDBACK_IMAGE_SUFFIXES = {".jpg", ".jpeg", ".png", ".gif", ".webp", ".heic"}