diff --git a/gpx-rs/engine/src/engine/command/file/delete.rs b/gpx-rs/engine/src/engine/command/file/delete.rs
index d1aa610f7..84cc16ad6 100644
--- a/gpx-rs/engine/src/engine/command/file/delete.rs
+++ b/gpx-rs/engine/src/engine/command/file/delete.rs
@@ -1,11 +1,153 @@
-use crate::{Apply, CommandError, State};
+use std::rc::Rc;
+
+use crate::{Apply, CommandError, Selection, State};
 
 #[derive(Debug)]
 pub struct Delete;
 
 impl Apply for Delete {
-    fn apply(self, _state: &mut State) -> Result<(), CommandError> {
-        // TODO
-        Err(CommandError::NotImplemented("delete"))
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let next = match &*state.selection {
+            Selection::File { file_ids } => {
+                state.files.retain(|id, _| !file_ids.contains(id));
+                state.order.0.retain(|id| !file_ids.contains(id));
+                Selection::Empty
+            }
+            Selection::Track { file_id, trk_ids } => {
+                let file = state
+                    .files
+                    .get_mut(file_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let file = Rc::make_mut(file);
+                let len = file.trk.len();
+                file.trk.retain(|trk| !trk_ids.contains(&trk.id));
+                if file.trk.len() == len {
+                    return Err(CommandError::NothingToDo);
+                }
+                Selection::File {
+                    file_ids: [*file_id].into(),
+                }
+            }
+            Selection::TrackSegment {
+                file_id,
+                trk_id,
+                trkseg_ids,
+            } => {
+                let file = state
+                    .files
+                    .get_mut(file_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let file = Rc::make_mut(file);
+                let trk = file
+                    .trk
+                    .iter_mut()
+                    .find(|trk| trk.id == *trk_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let len = trk.trkseg.len();
+                trk.trkseg.retain(|seg| !trkseg_ids.contains(&seg.id));
+                if trk.trkseg.len() == len {
+                    return Err(CommandError::NothingToDo);
+                }
+                Selection::Track {
+                    file_id: *file_id,
+                    trk_ids: [*trk_id].into(),
+                }
+            }
+            // TODO waypoints
+            Selection::Empty | Selection::Waypoints { .. } | Selection::Waypoint { .. } => {
+                return Err(CommandError::NothingToDo);
+            }
+        };
+        *state.selection = next;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::engine::command::fixture::Fixture;
+    use crate::{FileId, Load};
+
+    use super::*;
+
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load { data: &data }.apply(&mut fx.state()).unwrap();
+        let id = fx.order.0[0];
+        (fx, id)
+    }
+
+    #[test]
+    fn test_delete_nothing_selected() {
+        let mut fx = Fixture::default();
+        assert_eq!(
+            Delete.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_delete_selected_files() {
+        let (mut fx, id) = loaded();
+        crate::New { name: "keep" }.apply(&mut fx.state()).unwrap();
+        let keep = fx.order.0[1];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        Delete.apply(&mut fx.state()).unwrap();
+        assert_eq!(fx.order.0, vec![keep]);
+        assert!(fx.files.contains_key(&keep) && !fx.files.contains_key(&id));
+        assert!(matches!(fx.selection, Selection::Empty));
+    }
+
+    #[test]
+    fn test_delete_selected_tracks() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].trk.len();
+        let trk_id = fx.files[&id].trk[0].id;
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: HashSet::from([trk_id]),
+        };
+        Delete.apply(&mut fx.state()).unwrap();
+        let file = &fx.files[&id];
+        assert_eq!(file.trk.len(), before - 1);
+        assert!(file.trk.iter().all(|t| t.id != trk_id));
+        assert_eq!(fx.selected_files(), HashSet::from([id]));
+    }
+
+    #[test]
+    fn test_delete_selected_segments() {
+        let (mut fx, id) = loaded();
+        let trk = &fx.files[&id].trk[0];
+        let (trk_id, seg_id, before) = (trk.id, trk.trkseg[0].id, trk.trkseg.len());
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id,
+            trkseg_ids: HashSet::from([seg_id]),
+        };
+        Delete.apply(&mut fx.state()).unwrap();
+        let trk = &fx.files[&id].trk[0];
+        assert_eq!(trk.trkseg.len(), before - 1);
+        assert!(trk.trkseg.iter().all(|s| s.id != seg_id));
+        assert!(
+            matches!(&fx.selection, Selection::Track { trk_ids, .. } if trk_ids.contains(&trk_id))
+        );
+    }
+
+    #[test]
+    fn test_delete_unknown_ids_is_nothing_to_do() {
+        let (mut fx, id) = loaded();
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: HashSet::from([Default::default()]),
+        };
+        assert_eq!(
+            Delete.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
     }
 }
diff --git a/gpx-rs/engine/src/engine/command/file/duplicate.rs b/gpx-rs/engine/src/engine/command/file/duplicate.rs
index 846932339..ed9544837 100644
--- a/gpx-rs/engine/src/engine/command/file/duplicate.rs
+++ b/gpx-rs/engine/src/engine/command/file/duplicate.rs
@@ -1,11 +1,218 @@
-use crate::{Apply, CommandError, State};
+use std::{collections::HashSet, rc::Rc};
+
+use crate::{Apply, CommandError, File, Selection, State, Track, TrackSegment};
 
 #[derive(Debug)]
 pub struct Duplicate;
 
 impl Apply for Duplicate {
-    fn apply(self, _state: &mut State) -> Result<(), CommandError> {
-        // TODO
-        Err(CommandError::NotImplemented("duplicate"))
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let next = match &*state.selection {
+            Selection::File { file_ids } => {
+                let mut copies = HashSet::new();
+                let mut order = Vec::with_capacity(state.order.0.len() + file_ids.len());
+                for id in &state.order.0 {
+                    order.push(*id);
+                    let Some(file) = state.files.get(id).filter(|_| file_ids.contains(id)) else {
+                        continue;
+                    };
+                    let copy = copy_file(file);
+                    order.push(copy.id);
+                    copies.insert(copy.id);
+                    state.files.insert(copy.id, Rc::new(copy));
+                }
+                if copies.is_empty() {
+                    return Err(CommandError::NothingToDo);
+                }
+                state.order.0 = order;
+                Selection::File { file_ids: copies }
+            }
+            Selection::Track { file_id, trk_ids } => {
+                let file = state
+                    .files
+                    .get_mut(file_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let file = Rc::make_mut(file);
+                let mut copies = HashSet::new();
+                duplicate_after(
+                    &mut file.trk,
+                    |trk| trk_ids.contains(&trk.id),
+                    |trk| {
+                        let copy = copy_track(trk);
+                        copies.insert(copy.id);
+                        copy
+                    },
+                );
+                if copies.is_empty() {
+                    return Err(CommandError::NothingToDo);
+                }
+                Selection::Track {
+                    file_id: *file_id,
+                    trk_ids: copies,
+                }
+            }
+            Selection::TrackSegment {
+                file_id,
+                trk_id,
+                trkseg_ids,
+            } => {
+                let file = state
+                    .files
+                    .get_mut(file_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let file = Rc::make_mut(file);
+                let trk = file
+                    .trk
+                    .iter_mut()
+                    .find(|trk| trk.id == *trk_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let mut copies = HashSet::new();
+                duplicate_after(
+                    &mut trk.trkseg,
+                    |seg| trkseg_ids.contains(&seg.id),
+                    |seg| {
+                        let copy = copy_segment(seg);
+                        copies.insert(copy.id);
+                        copy
+                    },
+                );
+                if copies.is_empty() {
+                    return Err(CommandError::NothingToDo);
+                }
+                Selection::TrackSegment {
+                    file_id: *file_id,
+                    trk_id: *trk_id,
+                    trkseg_ids: copies,
+                }
+            }
+            // TODO waypoints
+            Selection::Empty | Selection::Waypoints { .. } | Selection::Waypoint { .. } => {
+                return Err(CommandError::NothingToDo);
+            }
+        };
+        *state.selection = next;
+        Ok(())
+    }
+}
+
+/// Inserts a copy right after each item matching `filter`.
+fn duplicate_after<T>(
+    items: &mut Vec<T>,
+    filter: impl Fn(&T) -> bool,
+    mut copy: impl FnMut(&T) -> T,
+) {
+    let old = std::mem::take(items);
+    for item in old {
+        let dup = filter(&item).then(|| copy(&item));
+        items.push(item);
+        items.extend(dup);
+    }
+}
+
+// Track points are shared chunks, so copies are cheap.
+fn copy_segment(segment: &TrackSegment) -> TrackSegment {
+    let mut copy = segment.clone();
+    copy.id = Default::default();
+    copy
+}
+
+fn copy_track(track: &Track) -> Track {
+    Track {
+        id: Default::default(),
+        trkseg: track.trkseg.iter().map(copy_segment).collect(),
+        ..track.clone()
+    }
+}
+
+fn copy_file(file: &File) -> File {
+    let mut copy = File {
+        id: Default::default(),
+        trk: file.trk.iter().map(copy_track).collect(),
+        ..file.clone()
+    };
+    copy.info.name = format!("{} (copy)", file.info.name);
+    copy
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::engine::command::fixture::Fixture;
+    use crate::{FileId, Load};
+
+    use super::*;
+
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load { data: &data }.apply(&mut fx.state()).unwrap();
+        let id = fx.order.0[0];
+        (fx, id)
+    }
+
+    #[test]
+    fn test_duplicate_nothing_selected() {
+        let mut fx = Fixture::default();
+        assert_eq!(
+            Duplicate.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_duplicate_file() {
+        let (mut fx, id) = loaded();
+        Duplicate.apply(&mut fx.state()).unwrap();
+        assert_eq!(fx.files.len(), 2);
+        let copy_id = fx.order.0[1];
+        assert_eq!(fx.selected_files(), [copy_id].into());
+        let (orig, copy) = (&fx.files[&id], &fx.files[&copy_id]);
+        assert_ne!(copy_id, id);
+        assert_eq!(copy.info.name, format!("{} (copy)", orig.info.name));
+        assert_eq!(copy.trk.len(), orig.trk.len());
+        for (a, b) in orig.trk.iter().zip(&copy.trk) {
+            assert_ne!(a.id, b.id);
+            assert_eq!(a.info, b.info);
+            for (a, b) in a.trkseg.iter().zip(&b.trkseg) {
+                assert_ne!(a.id, b.id);
+                assert_eq!(a.len(), b.len());
+            }
+        }
+    }
+
+    #[test]
+    fn test_duplicate_track_inserts_after_original() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].trk.len();
+        let trk_id = fx.files[&id].trk[0].id;
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: [trk_id].into(),
+        };
+        Duplicate.apply(&mut fx.state()).unwrap();
+        let file = &fx.files[&id];
+        assert_eq!(file.trk.len(), before + 1);
+        assert_eq!(file.trk[0].id, trk_id);
+        assert_ne!(file.trk[1].id, trk_id);
+        assert!(
+            matches!(&fx.selection, Selection::Track { trk_ids, .. } if trk_ids.contains(&file.trk[1].id))
+        );
+    }
+
+    #[test]
+    fn test_duplicate_segment_inserts_after_original() {
+        let (mut fx, id) = loaded();
+        let trk = &fx.files[&id].trk[0];
+        let (trk_id, seg_id, before) = (trk.id, trk.trkseg[0].id, trk.trkseg.len());
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id,
+            trkseg_ids: [seg_id].into(),
+        };
+        Duplicate.apply(&mut fx.state()).unwrap();
+        let trk = &fx.files[&id].trk[0];
+        assert_eq!(trk.trkseg.len(), before + 1);
+        assert_eq!(trk.trkseg[0].id, seg_id);
+        assert_ne!(trk.trkseg[1].id, seg_id);
+        assert_eq!(trk.trkseg[0].len(), trk.trkseg[1].len());
     }
 }
diff --git a/gpx-rs/engine/src/engine/engine.rs b/gpx-rs/engine/src/engine/engine.rs
index 07f3e3eb6..105f2d9cc 100644
--- a/gpx-rs/engine/src/engine/engine.rs
+++ b/gpx-rs/engine/src/engine/engine.rs
@@ -74,20 +74,6 @@ impl Engine {
     /// Brings everything derived from the files back in line with the current stack entry.
     fn refresh(&mut self) {
         let current = self.stack.current();
-        match current {
-            Some(files) => {
-                self.order.0.retain(|id| files.contains_key(id));
-                let known: HashSet<FileId> = self.order.0.iter().copied().collect();
-                self.order
-                    .0
-                    .extend(files.keys().filter(|id| !known.contains(id)).copied());
-                self.selection.retain_existing(files);
-            }
-            None => {
-                self.order.0.clear();
-                self.selection = Selection::Empty;
-            }
-        }
         self.statistics_cache.update(current);
         self.statistics_buffer
             .update(&self.statistics_cache.get(current, &self.selection));