diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a7664f3..ec8a574 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,7 +27,7 @@ jobs:
       - name: Install (with Celery + Django adapters)
         run: |
           python -m pip install --upgrade pip
-          pip install -e ".[dev,celery,django]"
+          pip install -e ".[dev,celery,django,otel]" opentelemetry-sdk
 
       - name: Run tests
         run: pytest
@@ -44,7 +44,7 @@ jobs:
       - name: Install (dev + all adapters for type context)
         run: |
           python -m pip install --upgrade pip
-          pip install -e ".[dev,celery,django,redis,amqp,sqs,azureservicebus,artemis]"
+          pip install -e ".[dev,celery,django,redis,amqp,sqs,azureservicebus,artemis,otel]" opentelemetry-sdk
       - name: Ruff
         run: ruff check src tests
       - name: Mypy
@@ -89,7 +89,7 @@ jobs:
       - name: Install (all adapters — full coverage with brokers)
         run: |
           python -m pip install --upgrade pip
-          pip install -e ".[redis,amqp,sqs,azureservicebus,artemis,celery,django,dev]"
+          pip install -e ".[redis,amqp,sqs,azureservicebus,artemis,celery,django,dev,otel]" opentelemetry-sdk
 
       - name: Wait for ElasticMQ
         run: |
diff --git a/pyproject.toml b/pyproject.toml
index 14b27b6..46ac30c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -36,6 +36,7 @@ azureservicebus = ["azure-servicebus>=7.11", "azure-identity>=1.15"]
 pulsar = ["pulsar-client>=3.4"]
 kafka = ["confluent-kafka>=2.3"]
 artemis = ["python-qpid-proton>=0.39"]
+otel = ["opentelemetry-api>=1.20"]
 celery = ["celery>=5"]
 django = ["django>=4.2"]
 dev = ["pytest>=7", "pytest-cov>=4", "mypy>=1.8", "ruff>=0.5"]
diff --git a/src/babelqueue/otel.py b/src/babelqueue/otel.py
new file mode 100644
index 0000000..09a4936
--- /dev/null
+++ b/src/babelqueue/otel.py
@@ -0,0 +1,176 @@
+"""Optional OpenTelemetry tracing (ADR-0025): produce/consume spans correlated across hops.
+
+The Python mirror of the Go ``babelqueue-go/otel`` module. It emits a CONSUMER span per
+handled message and a PRODUCER span per publish, correlating them across every hop and SDK
+through the envelope's ``trace_id`` — a UUID, which maps 1:1 to a 128-bit OTel trace id. The
+wire envelope is untouched (GR-1) and the core never imports OpenTelemetry: this module is
+only importable with the ``[otel]`` extra (``pip install babelqueue[otel]``), exactly like the
+optional transport drivers.
+
+    from opentelemetry import trace
+    from babelqueue import BabelQueue, otel
+
+    tracer = trace.get_tracer("orders")
+    app = BabelQueue("redis://localhost:6379/0", queue="orders")
+    app.register("urn:babel:orders:created", otel.wrap_handler(tracer, on_order_created))
+    # producer side:
+    otel.publish(tracer, app, "urn:babel:orders:created", {"order_id": 1042})
+
+Every hop that shares a ``trace_id`` shares one OTel trace. Exact cross-hop *span*
+parent-child linkage (W3C ``traceparent`` as a transport header) is a documented follow-up.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import inspect
+from typing import Any, Callable, Mapping, Optional
+
+from opentelemetry.context import Context
+from opentelemetry.trace import (
+    NonRecordingSpan,
+    SpanContext,
+    SpanKind,
+    TraceFlags,
+    Tracer,
+    set_span_in_context,
+)
+
+Handler = Callable[..., None]
+
+_SYSTEM = "babelqueue"
+_MASK_128 = (1 << 128) - 1
+
+
+def trace_id_of(trace_id: str) -> int:
+    """Map an envelope ``trace_id`` to a deterministic 128-bit OTel trace id.
+
+    A UUID maps to its 16 raw bytes; any other string is hashed (SHA-256, first 16 bytes).
+    The result is never zero (OTel's invalid trace id). The inverse of :func:`uuid_of` for
+    the UUID case.
+    """
+    raw = _uuid_bytes(trace_id)
+    if raw is not None:
+        n = int.from_bytes(raw, "big")
+        if n != 0:
+            return n
+    digest = hashlib.sha256(trace_id.encode("utf-8")).digest()[:16]
+    return int.from_bytes(digest, "big") or 1
+
+
+def uuid_of(trace_id_int: int) -> str:
+    """Format a 128-bit OTel trace id as a canonical UUID string.
+
+    The form a producer stamps into the message's ``trace_id`` so a consumer can recover the
+    same trace id via :func:`trace_id_of`.
+    """
+    h = format(trace_id_int & _MASK_128, "032x")
+    return f"{h[0:8]}-{h[8:12]}-{h[12:16]}-{h[16:20]}-{h[20:32]}"
+
+
+def _uuid_bytes(s: str) -> Optional[bytes]:
+    h = s.replace("-", "")
+    if len(h) != 32:
+        return None
+    try:
+        return bytes.fromhex(h)
+    except ValueError:
+        return None
+
+
+def _span_id_of(trace_id: str) -> int:
+    """Derive a deterministic, non-zero 64-bit span id so the remote parent context is valid
+    (a span needs a valid parent to inherit a specific trace)."""
+    digest = hashlib.sha256(("babelqueue-span:" + trace_id).encode("utf-8")).digest()[:8]
+    return int.from_bytes(digest, "big") or 1
+
+
+def _parent_context(trace_id: str) -> Context:
+    sc = SpanContext(
+        trace_id=trace_id_of(trace_id),
+        span_id=_span_id_of(trace_id),
+        is_remote=True,
+        trace_flags=TraceFlags(TraceFlags.SAMPLED),
+    )
+    return set_span_in_context(NonRecordingSpan(sc))
+
+
+def _wants_envelope(fn: Handler) -> bool:
+    """True if ``fn`` takes a 3rd positional arg (the full envelope) or ``*args``."""
+    try:
+        params = list(inspect.signature(fn).parameters.values())
+    except (TypeError, ValueError):  # pragma: no cover - builtins / C callables
+        return False
+    positional = [
+        p for p in params if p.kind in (p.POSITIONAL_ONLY, p.POSITIONAL_OR_KEYWORD)
+    ]
+    return any(p.kind == p.VAR_POSITIONAL for p in params) or len(positional) >= 3
+
+
+def wrap_handler(tracer: Tracer, handler: Handler) -> Handler:
+    """Wrap a consume handler to emit a CONSUMER span per message, in the OTel trace derived
+    from the envelope's ``trace_id``.
+
+    Register it like any handler: ``app.register(urn, wrap_handler(tracer, handler))``. The
+    wrapper's ``*args`` signature makes the runtime pass the full envelope (``data, meta,
+    envelope``), so it can read ``trace_id``/``job`` even when the inner handler only wants
+    ``(data, meta)``. A raising handler records the exception on the span and re-raises, so the
+    runtime's retry / dead-letter path still applies.
+    """
+
+    def wrapped(*args: Any) -> None:
+        envelope = args[2] if len(args) > 2 and isinstance(args[2], Mapping) else {}
+        meta = args[1] if len(args) > 1 and isinstance(args[1], Mapping) else {}
+        trace_id = str(envelope.get("trace_id") or "")
+        urn = str(envelope.get("job") or envelope.get("urn") or "")
+
+        attributes: dict[str, Any] = {
+            "messaging.system": _SYSTEM,
+            "messaging.operation": "process",
+            "messaging.destination.name": str(meta.get("queue") or ""),
+            "messaging.message.id": str(meta.get("id") or ""),
+            "messaging.message.conversation_id": trace_id,
+            "messaging.babelqueue.attempts": int(envelope.get("attempts", 0) or 0),
+        }
+        context = _parent_context(trace_id) if trace_id else None
+
+        with tracer.start_as_current_span(
+            "process " + urn,
+            context=context,
+            kind=SpanKind.CONSUMER,
+            attributes=attributes,
+        ):
+            if _wants_envelope(handler):
+                handler(*args)
+            else:
+                handler(args[0], args[1])
+
+    return wrapped
+
+
+def publish(
+    tracer: Tracer,
+    app: Any,
+    urn: str,
+    data: Mapping[str, Any],
+    *,
+    queue: Optional[str] = None,
+) -> str:
+    """Publish via a PRODUCER span ``publish <urn>``, carrying the active trace's id into the
+    message's ``trace_id`` so the downstream consumer recovers the same trace.
+
+    Behaves like ``app.publish`` (returns the message id); ``app`` is any object exposing
+    ``publish(urn, data, *, queue=None, trace_id=None) -> str``.
+    """
+    attributes = {
+        "messaging.system": _SYSTEM,
+        "messaging.operation": "publish",
+        "messaging.destination.name": urn,
+    }
+    with tracer.start_as_current_span(
+        "publish " + urn, kind=SpanKind.PRODUCER, attributes=attributes
+    ) as span:
+        trace_id = uuid_of(span.get_span_context().trace_id)
+        message_id = app.publish(urn, data, queue=queue, trace_id=trace_id)
+        span.set_attribute("messaging.message.id", message_id)
+        return message_id
diff --git a/tests/test_otel.py b/tests/test_otel.py
new file mode 100644
index 0000000..bf189f0
--- /dev/null
+++ b/tests/test_otel.py
@@ -0,0 +1,131 @@
+"""Tests for the optional OpenTelemetry module (ADR-0025).
+
+Skipped when OpenTelemetry is not installed (the ``[otel]`` extra); CI installs it so these
+run and count toward coverage.
+"""
+
+import pytest
+
+pytest.importorskip("opentelemetry")
+
+from opentelemetry.sdk.trace import TracerProvider  # noqa: E402
+from opentelemetry.sdk.trace.export import SimpleSpanProcessor  # noqa: E402
+from opentelemetry.sdk.trace.export.in_memory_span_exporter import (  # noqa: E402
+    InMemorySpanExporter,
+)
+from opentelemetry.trace import SpanKind  # noqa: E402
+
+from babelqueue import otel  # noqa: E402
+
+_TRACE_ID = "7b3f9c2a-e41d-4f88-9b2a-1c0d5e6f7a8b"
+
+
+def _recorder():
+    exporter = InMemorySpanExporter()
+    provider = TracerProvider()
+    provider.add_span_processor(SimpleSpanProcessor(exporter))
+    return provider.get_tracer("test"), exporter
+
+
+def _envelope(trace_id=_TRACE_ID, attempts=0):
+    return {
+        "job": "urn:babel:orders:created",
+        "trace_id": trace_id,
+        "data": {"order_id": 1},
+        "meta": {"id": "m1", "queue": "orders"},
+        "attempts": attempts,
+    }
+
+
+class FakeApp:
+    """An object exposing publish(urn, data, *, queue, trace_id) -> str, recording calls."""
+
+    def __init__(self):
+        self.calls = []
+
+    def publish(self, urn, data, *, queue=None, trace_id=None):
+        self.calls.append({"urn": urn, "data": data, "queue": queue, "trace_id": trace_id})
+        return "msg-123"
+
+
+def test_trace_id_round_trip():
+    tid = otel.trace_id_of(_TRACE_ID)
+    assert tid != 0
+    assert otel.uuid_of(tid) == _TRACE_ID
+    # a non-uuid trace_id maps deterministically to a valid, distinct trace id
+    assert otel.trace_id_of("not-a-uuid") == otel.trace_id_of("not-a-uuid")
+    assert otel.trace_id_of("not-a-uuid") != 0
+    assert otel.trace_id_of("not-a-uuid") != tid
+    # 32 chars but not hex → not a UUID, so it is hashed
+    assert otel.trace_id_of("z" * 32) != 0
+
+
+def test_wrap_handler_span_in_trace_with_attrs():
+    tracer, exporter = _recorder()
+    seen = {}
+
+    def handler(data, meta, envelope):
+        seen["called"] = True
+
+    env = _envelope()
+    otel.wrap_handler(tracer, handler)(env["data"], env["meta"], env)
+
+    assert seen.get("called")
+    spans = exporter.get_finished_spans()
+    assert len(spans) == 1
+    span = spans[0]
+    assert span.name == "process urn:babel:orders:created"
+    assert span.kind == SpanKind.CONSUMER
+    assert span.context.trace_id == otel.trace_id_of(_TRACE_ID)
+    assert span.attributes["messaging.message.conversation_id"] == _TRACE_ID
+    assert span.attributes["messaging.message.id"] == "m1"
+    assert span.attributes["messaging.destination.name"] == "orders"
+
+
+def test_wrap_handler_two_arg_inner():
+    tracer, exporter = _recorder()
+    got = {}
+
+    def handler(data, meta):  # only two positional args
+        got["data"] = data
+
+    env = _envelope()
+    # the runtime passes (data, meta, envelope); the wrapper forwards only what the inner wants
+    otel.wrap_handler(tracer, handler)(env["data"], env["meta"], env)
+
+    assert got["data"] == env["data"]
+    assert len(exporter.get_finished_spans()) == 1
+
+
+def test_wrap_handler_records_error():
+    tracer, exporter = _recorder()
+
+    def handler(data, meta, envelope):
+        raise ValueError("boom")
+
+    env = _envelope()
+    with pytest.raises(ValueError):
+        otel.wrap_handler(tracer, handler)(env["data"], env["meta"], env)
+
+    span = exporter.get_finished_spans()[0]
+    assert span.status.status_code.name == "ERROR"
+    assert len(span.events) >= 1  # the recorded exception
+
+
+def test_publish_stamps_trace_id_from_span():
+    tracer, exporter = _recorder()
+    app = FakeApp()
+
+    message_id = otel.publish(tracer, app, "urn:babel:orders:created", {"order_id": 7})
+
+    assert message_id == "msg-123"
+    spans = exporter.get_finished_spans()
+    assert len(spans) == 1
+    span = spans[0]
+    assert span.kind == SpanKind.PRODUCER
+    assert span.attributes["messaging.message.id"] == "msg-123"
+
+    stamped = app.calls[0]["trace_id"]
+    # the published trace_id encodes the producer span's trace, so a consumer recovers it
+    assert stamped == otel.uuid_of(span.context.trace_id)
+    assert otel.trace_id_of(stamped) == span.context.trace_id