diff --git a/src/data.rs b/src/data.rs
index 3e92cff..81ea80d 100644
--- a/src/data.rs
+++ b/src/data.rs
@@ -66,7 +66,7 @@ pub struct ItemLink {
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Deserialize, Serialize)]
 pub struct FieldID(usize);
 
-#[derive(Debug, Clone, Deserialize, Serialize)]
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Deserialize, Serialize)]
 pub struct FieldSchema {
     // Field names that may potentially exist on a given item. They are not
     // necessarily all present on any given item
@@ -165,7 +165,7 @@ pub struct ItemMeta {
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Deserialize, Serialize)]
 pub struct TileID(pub Interval);
 
-#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[derive(Debug, Clone, Default, PartialEq, Eq, PartialOrd, Ord, Deserialize, Serialize)]
 pub struct TileSet {
     pub tiles: Vec<Vec<TileID>>,
 }
@@ -443,3 +443,15 @@ impl fmt::Display for TileIDSlug {
         write!(f, "{}", self.0 .0.stop.0)
     }
 }
+
+// Private helpers for EntryID
+impl EntryID {
+    pub(crate) fn shift_level0(&self, level0_offset: i64) -> EntryID {
+        assert!(!self.0.is_empty());
+        assert_ne!(self.0[0], -1);
+        let mut result = self.clone();
+        result.0[0] += level0_offset;
+        assert!(result.0[0] >= 0);
+        result
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index fb87ed2..753c67b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,6 +8,7 @@ pub mod deferred_data;
 #[cfg(not(target_arch = "wasm32"))]
 pub mod file_data;
 pub mod http;
+pub mod merge_data;
 #[cfg(not(target_arch = "wasm32"))]
 pub mod parallel_data;
 pub mod timestamp;
diff --git a/src/merge_data.rs b/src/merge_data.rs
new file mode 100644
index 0000000..7203aee
--- /dev/null
+++ b/src/merge_data.rs
@@ -0,0 +1,292 @@
+use std::collections::VecDeque;
+
+use crate::data::{
+    DataSourceInfo, EntryID, EntryIndex, EntryInfo, Field, ItemLink, ItemUID, SlotMetaTile,
+    SlotTile, SummaryTile, TileID,
+};
+use crate::deferred_data::DeferredDataSource;
+use crate::timestamp::Interval;
+
+pub struct MergeDeferredDataSource {
+    data_sources: Vec<Box<dyn DeferredDataSource>>,
+    infos: Vec<VecDeque<DataSourceInfo>>,
+    mapping: Vec<u64>,
+}
+
+impl MergeDeferredDataSource {
+    pub fn new(data_sources: Vec<Box<dyn DeferredDataSource>>) -> Self {
+        assert!(!data_sources.is_empty());
+        let infos = (0..data_sources.len()).map(|_| VecDeque::new()).collect();
+        Self {
+            data_sources,
+            infos,
+            mapping: Vec::new(),
+        }
+    }
+
+    fn merge_entry(first: EntryInfo, second: EntryInfo) -> EntryInfo {
+        let EntryInfo::Panel {
+            short_name,
+            long_name,
+            summary: first_summary,
+            mut slots,
+        } = first
+        else {
+            unreachable!();
+        };
+
+        let EntryInfo::Panel {
+            summary: second_summary,
+            slots: second_slots,
+            ..
+        } = second
+        else {
+            unreachable!();
+        };
+
+        assert!(first_summary.is_none());
+        assert!(second_summary.is_none());
+
+        slots.extend(second_slots);
+
+        EntryInfo::Panel {
+            short_name,
+            long_name,
+            summary: None,
+            slots,
+        }
+    }
+
+    fn compute_mapping(source_infos: &[DataSourceInfo]) -> Vec<u64> {
+        // Compute the mapping from old to new entries (basically the offset
+        // of each initial slot)
+        let slot_lens: Vec<_> = source_infos
+            .iter()
+            .map(|info| {
+                let EntryInfo::Panel { ref slots, .. } = info.entry_info else {
+                    unreachable!();
+                };
+                slots.len() as u64
+            })
+            .collect();
+
+        let mut mapping = Vec::new();
+        let mut sum = 0;
+        for slot_len in slot_lens {
+            mapping.push(sum);
+            sum += slot_len;
+        }
+
+        mapping
+    }
+
+    fn merge_infos(source_infos: Vec<DataSourceInfo>) -> DataSourceInfo {
+        assert!(!source_infos.is_empty());
+
+        // Some fields can't be meaningfully merged, so just assert they're
+        // all equivalent.
+        let first_info = source_infos.first().unwrap();
+        let tile_set = first_info.tile_set.clone();
+        let field_schema = first_info.field_schema.clone();
+
+        for info in &source_infos {
+            assert_eq!(tile_set, info.tile_set);
+            assert_eq!(field_schema, info.field_schema);
+        }
+
+        // Merge remaining fields
+        // IMPORTANT: entry_info must be kept consistent with compute_mapping
+        let interval = source_infos
+            .iter()
+            .map(|info| info.interval)
+            .reduce(Interval::union)
+            .unwrap();
+        let entry_info = source_infos
+            .iter()
+            .map(|info| info.entry_info.clone())
+            .reduce(Self::merge_entry)
+            .unwrap();
+
+        DataSourceInfo {
+            entry_info,
+            interval,
+            tile_set,
+            field_schema,
+        }
+    }
+
+    fn map_src_to_dst_entry(&self, idx: usize, src_entry: &EntryID) -> EntryID {
+        src_entry.shift_level0(self.mapping[idx] as i64)
+    }
+
+    fn map_dst_to_src_entry(&self, dst_entry: &EntryID) -> (usize, EntryID) {
+        let Some(EntryIndex::Slot(level0)) = dst_entry.index(0) else {
+            unreachable!();
+        };
+
+        let idx = self.mapping.partition_point(|&offset| offset < level0);
+        (idx, dst_entry.shift_level0(-(self.mapping[idx] as i64)))
+    }
+
+    fn map_src_to_dst_item_uid(&self, idx: usize, item_uid: ItemUID) -> ItemUID {
+        ItemUID(item_uid.0 * (self.mapping.len() as u64) + (idx as u64))
+    }
+
+    fn map_src_to_dst_summary(&self, idx: usize, tile: SummaryTile) -> SummaryTile {
+        SummaryTile {
+            entry_id: self.map_src_to_dst_entry(idx, &tile.entry_id),
+            tile_id: tile.tile_id,
+            data: tile.data,
+        }
+    }
+
+    fn map_src_to_dst_slot(&self, idx: usize, mut tile: SlotTile) -> SlotTile {
+        for items in &mut tile.data.items {
+            for item in items {
+                item.item_uid = self.map_src_to_dst_item_uid(idx, item.item_uid);
+            }
+        }
+
+        SlotTile {
+            entry_id: self.map_src_to_dst_entry(idx, &tile.entry_id),
+            tile_id: tile.tile_id,
+            data: tile.data,
+        }
+    }
+
+    fn map_src_to_dst_field(&self, idx: usize, field: &mut Field) {
+        match field {
+            Field::ItemLink(ItemLink {
+                ref mut item_uid,
+                ref mut entry_id,
+                ..
+            }) => {
+                *item_uid = self.map_src_to_dst_item_uid(idx, *item_uid);
+                *entry_id = self.map_src_to_dst_entry(idx, entry_id);
+            }
+            Field::Vec(elts) => {
+                for elt in elts {
+                    self.map_src_to_dst_field(idx, elt);
+                }
+            }
+            _ => (),
+        }
+    }
+
+    fn map_src_to_dst_slot_meta(&self, idx: usize, mut tile: SlotMetaTile) -> SlotMetaTile {
+        for items in &mut tile.data.items {
+            for item in items {
+                item.item_uid = self.map_src_to_dst_item_uid(idx, item.item_uid);
+                for (_, field) in &mut item.fields {
+                    self.map_src_to_dst_field(idx, field);
+                }
+            }
+        }
+
+        SlotMetaTile {
+            entry_id: self.map_src_to_dst_entry(idx, &tile.entry_id),
+            tile_id: tile.tile_id,
+            data: tile.data,
+        }
+    }
+}
+
+impl DeferredDataSource for MergeDeferredDataSource {
+    fn fetch_info(&mut self) {
+        for data_source in &mut self.data_sources {
+            data_source.fetch_info();
+        }
+    }
+
+    fn get_infos(&mut self) -> Vec<DataSourceInfo> {
+        for (data_source, infos) in self.data_sources.iter_mut().zip(self.infos.iter_mut()) {
+            infos.extend(data_source.get_infos());
+        }
+
+        let max_available = self.infos.iter().map(|infos| infos.len()).max().unwrap();
+
+        let mut result = Vec::new();
+        for _ in 0..max_available {
+            let source_infos: Vec<_> = self
+                .infos
+                .iter_mut()
+                .map(|infos| infos.pop_front().unwrap())
+                .collect();
+            self.mapping = Self::compute_mapping(&source_infos);
+            result.push(Self::merge_infos(source_infos));
+        }
+        result
+    }
+
+    fn fetch_summary_tile(&mut self, entry_id: &EntryID, tile_id: TileID, full: bool) {
+        let (idx, src_entry) = self.map_dst_to_src_entry(entry_id);
+
+        self.data_sources[idx].fetch_summary_tile(&src_entry, tile_id, full);
+    }
+
+    fn get_summary_tiles(&mut self) -> Vec<SummaryTile> {
+        let mut tiles = Vec::new();
+        for (idx, data_source) in self.data_sources.iter_mut().enumerate() {
+            tiles.extend(
+                data_source
+                    .get_summary_tiles()
+                    .into_iter()
+                    .map(|tile| (idx, tile)),
+            );
+        }
+
+        // Hack: doing this in two stages to avoid mutability conflict
+        tiles
+            .into_iter()
+            .map(|(idx, tile)| self.map_src_to_dst_summary(idx, tile))
+            .collect()
+    }
+
+    fn fetch_slot_tile(&mut self, entry_id: &EntryID, tile_id: TileID, full: bool) {
+        let (idx, src_entry) = self.map_dst_to_src_entry(entry_id);
+
+        self.data_sources[idx].fetch_slot_tile(&src_entry, tile_id, full);
+    }
+
+    fn get_slot_tiles(&mut self) -> Vec<SlotTile> {
+        let mut tiles = Vec::new();
+        for (idx, data_source) in self.data_sources.iter_mut().enumerate() {
+            tiles.extend(
+                data_source
+                    .get_slot_tiles()
+                    .into_iter()
+                    .map(|tile| (idx, tile)),
+            );
+        }
+
+        // Hack: doing this in two stages to avoid mutability conflict
+        tiles
+            .into_iter()
+            .map(|(idx, tile)| self.map_src_to_dst_slot(idx, tile))
+            .collect()
+    }
+
+    fn fetch_slot_meta_tile(&mut self, entry_id: &EntryID, tile_id: TileID, full: bool) {
+        let (idx, src_entry) = self.map_dst_to_src_entry(entry_id);
+
+        self.data_sources[idx].fetch_slot_meta_tile(&src_entry, tile_id, full);
+    }
+
+    fn get_slot_meta_tiles(&mut self) -> Vec<SlotMetaTile> {
+        let mut tiles = Vec::new();
+        for (idx, data_source) in self.data_sources.iter_mut().enumerate() {
+            tiles.extend(
+                data_source
+                    .get_slot_meta_tiles()
+                    .into_iter()
+                    .map(|tile| (idx, tile)),
+            );
+        }
+
+        // Hack: doing this in two stages to avoid mutability conflict
+        tiles
+            .into_iter()
+            .map(|(idx, tile)| self.map_src_to_dst_slot_meta(idx, tile))
+            .collect()
+    }
+}