diff --git a/lib/src/working_copy.rs b/lib/src/working_copy.rs
index b052e3122..b01d15891 100644
--- a/lib/src/working_copy.rs
+++ b/lib/src/working_copy.rs
@@ -38,7 +38,7 @@ use crate::commit::Commit;
 use crate::conflicts::{materialize_conflict, update_conflict_from_content};
 use crate::gitignore::GitIgnoreFile;
 use crate::lock::FileLock;
-use crate::matchers::EverythingMatcher;
+use crate::matchers::{EverythingMatcher, Matcher};
 use crate::repo_path::{RepoPath, RepoPathComponent, RepoPathJoin};
 use crate::store::Store;
 use crate::tree::Diff;
@@ -189,6 +189,16 @@ pub enum CheckoutError {
     InternalBackendError(BackendError),
 }
 
+#[derive(Debug, Error, PartialEq, Eq)]
+pub enum UntrackError {
+    // The current checkout was deleted, maybe by an overly aggressive GC that happened while
+    // the current process was running.
+    #[error("Current checkout not found")]
+    SourceNotFound,
+    #[error("Internal error: {0:?}")]
+    InternalBackendError(BackendError),
+}
+
 impl TreeState {
     pub fn current_tree_id(&self) -> &TreeId {
         &self.tree_id
@@ -662,6 +672,25 @@ impl TreeState {
         self.save();
         Ok(stats)
     }
+
+    pub fn untrack(&mut self, matcher: &dyn Matcher) -> Result<(), UntrackError> {
+        let tree = self
+            .store
+            .get_tree(&RepoPath::root(), &self.tree_id)
+            .map_err(|err| match err {
+                BackendError::NotFound => UntrackError::SourceNotFound,
+                other => UntrackError::InternalBackendError(other),
+            })?;
+
+        let mut tree_builder = self.store.tree_builder(self.tree_id.clone());
+        for (path, _value) in tree.entries_matching(matcher) {
+            self.file_states.remove(&path);
+            tree_builder.remove(path);
+        }
+        self.tree_id = tree_builder.write_tree();
+        self.save();
+        Ok(())
+    }
 }
 
 pub struct WorkingCopy {
@@ -831,6 +860,19 @@ impl WorkingCopy {
             closed: false,
         }
     }
+
+    pub fn untrack(&self, matcher: &dyn Matcher) -> Result<LockedWorkingCopy, UntrackError> {
+        let lock_path = self.state_path.join("working_copy.lock");
+        let lock = FileLock::lock(lock_path);
+
+        self.tree_state().as_mut().unwrap().untrack(matcher)?;
+
+        Ok(LockedWorkingCopy {
+            wc: self,
+            lock,
+            closed: false,
+        })
+    }
 }
 
 // A working copy that's locked on disk. The tree state has already been
diff --git a/lib/tests/test_working_copy.rs b/lib/tests/test_working_copy.rs
index f7371df39..d7432a91d 100644
--- a/lib/tests/test_working_copy.rs
+++ b/lib/tests/test_working_copy.rs
@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::collections::HashSet;
 use std::fs::{File, OpenOptions};
 use std::io::{Read, Write};
 #[cfg(unix)]
@@ -21,6 +22,7 @@ use std::sync::Arc;
 use itertools::Itertools;
 use jujutsu_lib::backend::{Conflict, ConflictPart, TreeValue};
 use jujutsu_lib::commit_builder::CommitBuilder;
+use jujutsu_lib::matchers::FilesMatcher;
 use jujutsu_lib::repo::ReadonlyRepo;
 use jujutsu_lib::repo_path::{RepoPath, RepoPathComponent};
 use jujutsu_lib::settings::UserSettings;
@@ -294,6 +296,68 @@ fn test_checkout_file_transitions(use_git: bool) {
     }
 }
 
+#[test]
+fn test_untrack() {
+    let settings = testutils::user_settings();
+    let (_temp_dir, repo) = testutils::init_repo(&settings, false);
+
+    let wanted_path = RepoPath::from_internal_string("wanted");
+    let unwanted_path = RepoPath::from_internal_string("unwanted");
+    let gitignore_path = RepoPath::from_internal_string(".gitignore");
+
+    // First create a commit where one of the files is unwanted.
+    let initial_tree = testutils::create_tree(
+        &repo,
+        &[
+            (&wanted_path, "code"),
+            (&unwanted_path, "garbage"),
+            (&gitignore_path, "unwanted\n"),
+        ],
+    );
+    let mut tx = repo.start_transaction("test");
+    let initial_commit = CommitBuilder::for_open_commit(
+        &settings,
+        repo.store(),
+        repo.store().root_commit_id().clone(),
+        initial_tree.id().clone(),
+    )
+    .write_to_repo(tx.mut_repo());
+    let repo = tx.commit();
+    let working_copy = repo.working_copy().clone();
+    let locked_working_copy = working_copy.lock().unwrap();
+    locked_working_copy
+        .check_out(initial_commit.clone())
+        .unwrap();
+
+    // Now we untrack the file called "unwanted"
+    let mut tx = repo.start_transaction("test");
+    let matcher = FilesMatcher::new(HashSet::from([unwanted_path.clone()]));
+    let unfinished_write = locked_working_copy.untrack(&matcher).unwrap();
+    let new_commit = CommitBuilder::for_rewrite_from(&settings, repo.store(), &initial_commit)
+        .set_tree(unfinished_write.new_tree_id())
+        .write_to_repo(tx.mut_repo());
+    unfinished_write.finish(new_commit.clone());
+    let repo = tx.commit();
+
+    // The file should still exist in the working copy.
+    assert!(unwanted_path.to_fs_path(repo.working_copy_path()).is_file());
+
+    // It should not be in the new tree.
+    let tracked_paths = new_commit
+        .tree()
+        .entries()
+        .map(|(path, _)| path)
+        .collect_vec();
+    assert_eq!(tracked_paths, vec![gitignore_path, wanted_path]);
+
+    // It should not get re-added if we write a new tree since we also added it
+    // to the .gitignore file.
+    let unfinished_write = locked_working_copy.write_tree();
+    let new_tree_id = unfinished_write.new_tree_id();
+    assert_eq!(new_tree_id, *new_commit.tree().id());
+    unfinished_write.discard();
+}
+
 #[test_case(false ; "local backend")]
 #[test_case(true ; "git backend")]
 fn test_commit_racy_timestamps(use_git: bool) {