diff --git a/josh-core/src/filter/mod.rs b/josh-core/src/filter/mod.rs
index a8ea2f10d..d6fc34b69 100644
--- a/josh-core/src/filter/mod.rs
+++ b/josh-core/src/filter/mod.rs
@@ -321,6 +321,10 @@ enum Op {
     Prefix(std::path::PathBuf),
     Subdir(std::path::PathBuf),
     Workspace(std::path::PathBuf),
+    #[cfg(feature = "incubating")]
+    Lookup(std::path::PathBuf),
+    #[cfg(feature = "incubating")]
+    Lookup2(git2::Oid),
     Stored(std::path::PathBuf),
 
     Pattern(String),
@@ -599,6 +603,14 @@ fn spec2(op: &Op) -> String {
         Op::Workspace(path) => {
             format!(":workspace={}", parse::quote_if(&path.to_string_lossy()))
         }
+        #[cfg(feature = "incubating")]
+        Op::Lookup(path) => {
+            format!(":lookup={}", parse::quote_if(&path.to_string_lossy()))
+        }
+        #[cfg(feature = "incubating")]
+        Op::Lookup2(oid) => {
+            format!(":lookup2={}", oid.to_string())
+        }
         Op::Stored(path) => {
             format!(":+{}", parse::quote_if(&path.to_string_lossy()))
         }
@@ -926,6 +938,71 @@ fn apply_to_commit2(
 
             apply(transaction, nf, Apply::from_commit(commit)?)?
         }
+        #[cfg(feature = "incubating")]
+        Op::Lookup(lookup_path) => {
+            let lookup_commit = if let Some(lookup_commit) =
+                apply_to_commit2(&Op::Subdir(lookup_path.clone()), &commit, transaction)?
+            {
+                lookup_commit
+            } else {
+                return Ok(None);
+            };
+
+            let op = Op::Lookup2(lookup_commit);
+
+            if let Some(start) = transaction.get(to_filter(op), commit.id()) {
+                transaction.insert(filter, commit.id(), start, true);
+                return Ok(Some(start));
+            } else {
+                return Ok(None);
+            }
+        }
+
+        #[cfg(feature = "incubating")]
+        Op::Lookup2(lookup_commit_id) => {
+            let lookup_commit = repo.find_commit(*lookup_commit_id)?;
+            for parent in lookup_commit.parents() {
+                let lookup_tree = lookup_commit.tree_id();
+                let cw = get_filter(
+                    transaction,
+                    &repo.find_tree(lookup_tree)?,
+                    &std::path::PathBuf::new().join(commit.id().to_string()),
+                );
+                if cw != filter::empty() {
+                    if let Some(start) =
+                        apply_to_commit2(&Op::Lookup2(parent.id()), &commit, transaction)?
+                    {
+                        transaction.insert(filter, commit.id(), start, true);
+                        return Ok(Some(start));
+                    } else {
+                        return Ok(None);
+                    }
+                }
+                break;
+            }
+            let lookup_tree = lookup_commit.tree_id();
+            let cw = get_filter(
+                transaction,
+                &repo.find_tree(lookup_tree)?,
+                &std::path::PathBuf::new().join(commit.id().to_string()),
+            );
+
+            if cw == filter::empty() {
+                // FIXME empty filter or no entry in table?
+                for parent in commit.parents() {
+                    if let Some(start) = apply_to_commit2(&op, &parent, transaction)? {
+                        transaction.insert(filter, commit.id(), start, true);
+                        return Ok(Some(start));
+                    } else {
+                        return Ok(None);
+                    }
+                }
+                return Ok(None);
+            }
+
+            Apply::from_commit(commit)?
+                .with_tree(apply(transaction, cw, Apply::from_commit(commit)?)?.into_tree())
+        }
         Op::Squash(Some(ids)) => {
             if let Some(sq) = ids.get(&LazyRef::Resolved(commit.id())) {
                 let oid = if let Some(oid) =
@@ -1717,6 +1794,8 @@ fn apply2<'a>(transaction: &'a cache::Transaction, op: &Op, x: Apply<'a>) -> Jos
             }
         }
         Op::Pin(_) => Ok(x),
+        #[cfg(feature = "incubating")]
+        Op::Lookup(_) | Op::Lookup2(_) => Err(josh_error("not applicable to tree")),
     }
 }
 
diff --git a/josh-core/src/filter/parse.rs b/josh-core/src/filter/parse.rs
index 5908649c2..07c8959b4 100644
--- a/josh-core/src/filter/parse.rs
+++ b/josh-core/src/filter/parse.rs
@@ -10,6 +10,8 @@ fn make_op(args: &[&str]) -> JoshResult<Op> {
         ["author", author, email] => Ok(Op::Author(author.to_string(), email.to_string())),
         ["committer", author, email] => Ok(Op::Committer(author.to_string(), email.to_string())),
         ["workspace", arg] => Ok(Op::Workspace(Path::new(arg).to_owned())),
+        #[cfg(feature = "incubating")]
+        ["lookup", arg] => Ok(Op::Lookup(Path::new(arg).to_owned())),
         ["prefix"] => Err(josh_error(indoc!(
             r#"
             Filter ":prefix" requires an argument.
diff --git a/josh-core/src/filter/persist.rs b/josh-core/src/filter/persist.rs
index aa0745dab..9157bd6a3 100644
--- a/josh-core/src/filter/persist.rs
+++ b/josh-core/src/filter/persist.rs
@@ -325,6 +325,16 @@ impl InMemoryBuilder {
                 let params_tree = self.build_str_params(&[hook.as_ref()]);
                 push_tree_entries(&mut entries, [("hook", params_tree)]);
             }
+            #[cfg(feature = "incubating")]
+            Op::Lookup(path) => {
+                let params_tree = self.build_str_params(&[path.to_string_lossy().as_ref()]);
+                push_tree_entries(&mut entries, [("lookup", params_tree)]);
+            }
+            #[cfg(feature = "incubating")]
+            Op::Lookup2(oid) => {
+                let params_tree = self.build_str_params(&[oid.to_string().as_ref()]);
+                push_tree_entries(&mut entries, [("lookup2", params_tree)]);
+            }
         }
 
         let tree = gix_object::Tree { entries };
@@ -606,6 +616,32 @@ fn from_tree2(repo: &git2::Repository, tree_oid: git2::Oid) -> JoshResult<Op> {
             let path = std::str::from_utf8(path_blob.content())?;
             Ok(Op::Stored(std::path::PathBuf::from(path)))
         }
+        #[cfg(feature = "incubating")]
+        "lookup" => {
+            let inner = repo.find_tree(entry.id())?;
+            let path_blob = repo.find_blob(
+                inner
+                    .get_name("0")
+                    .ok_or_else(|| josh_error("lookup: missing path"))?
+                    .id(),
+            )?;
+            let path = std::str::from_utf8(path_blob.content())?;
+            Ok(Op::Lookup(std::path::PathBuf::from(path)))
+        }
+        #[cfg(feature = "incubating")]
+        "lookup2" => {
+            let inner = repo.find_tree(entry.id())?;
+            let oid_blob = repo.find_blob(
+                inner
+                    .get_name("0")
+                    .ok_or_else(|| josh_error("lookup2: missing oid"))?
+                    .id(),
+            )?;
+            let oid_str = std::str::from_utf8(oid_blob.content())?;
+            let oid = git2::Oid::from_str(oid_str)
+                .map_err(|e| josh_error(&format!("lookup2: invalid oid: {}", e)))?;
+            Ok(Op::Lookup2(oid))
+        }
         "compose" => {
             let compose_tree = repo.find_tree(entry.id())?;
             let mut filters = Vec::new();
diff --git a/tests/experimental/lookup.t b/tests/experimental/lookup.t
new file mode 100644
index 000000000..efb64f4b6
--- /dev/null
+++ b/tests/experimental/lookup.t
@@ -0,0 +1,117 @@
+  $ export TERM=dumb
+  $ export RUST_LOG_STYLE=never
+
+  $ git init -q real_repo 1> /dev/null
+  $ cd real_repo
+
+  $ mkdir sub1
+  $ echo contents1 > sub1/file1
+  $ git add sub1
+  $ git commit -m "add file1" 1> /dev/null
+
+  $ mkdir sub1
+  mkdir: cannot create directory 'sub1': File exists
+  [1]
+  $ echo contents2 > sub1/file2
+  $ git add sub1
+  $ git commit -m "add file2" 1> /dev/null
+
+  $ git log --graph --pretty=%H
+  * 81b10fb4984d20142cd275b89c91c346e536876a
+  * bb282e9cdc1b972fffd08fd21eead43bc0c83cb8
+
+  $ mkdir table
+  $ echo ":prefix=x" > table/81b10fb4984d20142cd275b89c91c346e536876a
+  $ echo ":prefix=y" > table/bb282e9cdc1b972fffd08fd21eead43bc0c83cb8
+  $ git add table
+  $ git commit -m "add lookup table" 1> /dev/null
+
+
+  $ echo contents3 > sub1/file3
+  $ git add sub1
+  $ git commit -m "add file3" 1> /dev/null
+
+  $ git log --graph --pretty=%H
+  * 26e4c43675b985689e280bc42264a9226af76943
+  * 14c74c5eca73952b36d736034b388832748c49d6
+  * 81b10fb4984d20142cd275b89c91c346e536876a
+  * bb282e9cdc1b972fffd08fd21eead43bc0c83cb8
+
+  $ josh-filter -s ":lookup=table" --update refs/heads/filtered
+  [1] :lookup=table
+  [2] :/table
+  [4] :lookup2=4880528e9d57aa5efc925e120a8077bfa37d778d
+
+  $ git log refs/heads/filtered --graph --pretty=%s
+  * add file2
+  * add file1
+  $ git diff ${EMPTY_TREE}..refs/heads/filtered
+  diff --git a/x/sub1/file1 b/x/sub1/file1
+  new file mode 100644
+  index 0000000..a024003
+  --- /dev/null
+  +++ b/x/sub1/file1
+  @@ -0,0 +1 @@
+  +contents1
+  diff --git a/x/sub1/file2 b/x/sub1/file2
+  new file mode 100644
+  index 0000000..6b46faa
+  --- /dev/null
+  +++ b/x/sub1/file2
+  @@ -0,0 +1 @@
+  +contents2
+  $ git diff ${EMPTY_TREE}..refs/heads/filtered~1
+  diff --git a/y/sub1/file1 b/y/sub1/file1
+  new file mode 100644
+  index 0000000..a024003
+  --- /dev/null
+  +++ b/y/sub1/file1
+  @@ -0,0 +1 @@
+  +contents1
+
+  $ echo ":prefix=z" > table/14c74c5eca73952b36d736034b388832748c49d6
+  $ echo ":prefix=z" > table/26e4c43675b985689e280bc42264a9226af76943
+  $ git add table
+  $ git commit -m "mod lookup table" 1> /dev/null
+  $ tree table
+  table
+  |-- 14c74c5eca73952b36d736034b388832748c49d6
+  |-- 26e4c43675b985689e280bc42264a9226af76943
+  |-- 81b10fb4984d20142cd275b89c91c346e536876a
+  `-- bb282e9cdc1b972fffd08fd21eead43bc0c83cb8
+  
+  1 directory, 4 files
+
+  $ josh-filter -s ":lookup=table" --update refs/heads/filtered
+  Warning: reference refs/heads/filtered wasn't updated
+  [2] :lookup=table
+  [3] :/table
+  [4] :lookup2=4880528e9d57aa5efc925e120a8077bfa37d778d
+  [5] :lookup2=ed934c124e28c83270d9cfbb011f3ceb46c0f69e
+  $ git log refs/heads/filtered --graph --pretty=%s
+  * add file2
+  * add file1
+
+  $ git diff ${EMPTY_TREE}..refs/heads/filtered
+  diff --git a/x/sub1/file1 b/x/sub1/file1
+  new file mode 100644
+  index 0000000..a024003
+  --- /dev/null
+  +++ b/x/sub1/file1
+  @@ -0,0 +1 @@
+  +contents1
+  diff --git a/x/sub1/file2 b/x/sub1/file2
+  new file mode 100644
+  index 0000000..6b46faa
+  --- /dev/null
+  +++ b/x/sub1/file2
+  @@ -0,0 +1 @@
+  +contents2
+  $ git diff ${EMPTY_TREE}..refs/heads/filtered~1
+  diff --git a/y/sub1/file1 b/y/sub1/file1
+  new file mode 100644
+  index 0000000..a024003
+  --- /dev/null
+  +++ b/y/sub1/file1
+  @@ -0,0 +1 @@
+  +contents1