diff --git a/src/client/state/lanes.ts b/src/client/state/lanes.ts
new file mode 100644
index 0000000..13435f5
--- /dev/null
+++ b/src/client/state/lanes.ts
@@ -0,0 +1,83 @@
+import type { LaneId } from "../../shared/custom.ts";
+import { endingSoonestFirst, type EventClock } from "../../shared/time.ts";
+
+/**
+ * How the timeline is stacked: a lane per game, or every game together in
+ * deadline order.
+ *
+ * Two different questions, and one board cannot answer both. Lanes answer "how
+ * does this game's patch lay out?" — they keep a game's events adjacent and
+ * comparable, which is what makes the board readable for someone playing four
+ * of them. But a reader with four games also has one queue of deadlines, and
+ * lanes scatter it: the thing ending tonight sits three lanes below the thing
+ * ending next month, and no amount of scrolling puts them next to each other.
+ *
+ * Pure, and its own module rather than logic inside `Timeline`, because `prefs`
+ * stores the chosen mode and the two must agree on what is valid — the same
+ * reason `zoom.ts` exists.
+ */
+export type TimelineGroup = "game" | "ending";
+
+export const TIMELINE_GROUPS: Array<{
+  id: TimelineGroup;
+  label: string;
+  hint: string;
+}> = [
+  { id: "game", label: "By game", hint: "One lane per game" },
+  {
+    id: "ending",
+    label: "Ending soonest",
+    hint: "Every game together, in deadline order",
+  },
+];
+
+/** The shape this module needs. Structural, so it stays cheap to call. */
+interface Row {
+  event: { game: LaneId };
+  clock: EventClock;
+}
+
+/**
+ * One stack of bars on the board.
+ *
+ * `game` is null on the merged board, which is what tells the renderer to drop
+ * the lane heading and name the game on each bar instead: the colour alone
+ * cannot say which game an event belongs to once thirteen of them share a
+ * stack.
+ */
+export interface Lane<T> {
+  /** React key and lane identity — the game id, or `all` when merged. */
+  id: string;
+  game: LaneId | null;
+  rows: T[];
+}
+
+/**
+ * Stack the board's rows the way the reader asked for.
+ *
+ * The merged mode sorts with `endingSoonestFirst`, the same comparator the
+ * list's "Ending soonest" uses, rather than a bare end-date sort — otherwise
+ * the two views would mean different things by the same words, and an event
+ * that has not started yet would cut in above one that is running out tonight.
+ * It also carries the `endsAt: null` rule for free: an unannounced end sorts
+ * behind every dated one instead of pretending to a position in the queue.
+ *
+ * Lane mode leaves the order it was given alone. The rows arrive sorted by
+ * whatever the reader chose in the list, and grouping them by game is not a
+ * licence to re-sort inside a game.
+ */
+export function timelineLanes<T extends Row>(
+  rows: readonly T[],
+  mode: TimelineGroup,
+): Array<Lane<T>> {
+  if (mode === "ending") {
+    if (rows.length === 0) return [];
+    return [{ id: "all", game: null, rows: [...rows].sort(endingSoonestFirst) }];
+  }
+
+  const byGame = new Map<LaneId, T[]>();
+  for (const row of rows) {
+    byGame.set(row.event.game, [...(byGame.get(row.event.game) ?? []), row]);
+  }
+  return [...byGame].map(([game, laneRows]) => ({ id: game, game, rows: laneRows }));
+}
diff --git a/src/client/state/usePrefs.ts b/src/client/state/usePrefs.ts
index ac8316d..0cd94e7 100644
--- a/src/client/state/usePrefs.ts
+++ b/src/client/state/usePrefs.ts
@@ -4,6 +4,7 @@ import type { Region } from "../../shared/schema.ts";
 import { guessRegion } from "../../shared/time.ts";
 import type { SortMode } from "./sort.ts";
 import { KEYS, readJson, writeJson } from "./storage.ts";
+import type { TimelineGroup } from "./lanes.ts";
 import { DEFAULT_DAY_WIDTH } from "./zoom.ts";
 
 /**
@@ -72,6 +73,18 @@ export interface Prefs {
    * from an older export — or a corrupted one — land on something renderable.
    */
   timelineDayWidth: number;
+  /**
+   * How the timeline stacks its bars: a lane per game, or every game together
+   * in deadline order.
+   *
+   * Remembered for the same reason `view` and `timelineDayWidth` are — it is
+   * the reader's answer to "how do I read this?", and a board that went back to
+   * lanes on every reload would make them say it again each time.
+   *
+   * Defaults to `"game"`, which is the board every existing reader already has.
+   * A stored pref wins, so shipping this moves nobody's view.
+   */
+  timelineGroup: TimelineGroup;
   /**
    * Whether to guess which events repeat daily from what the source printed.
    * Off leaves only the ones the reader marked themselves; it never discards a
@@ -99,6 +112,7 @@ function defaults(): Prefs {
     sort: "ending",
     view: "soon",
     timelineDayWidth: DEFAULT_DAY_WIDTH,
+    timelineGroup: "game",
     detectDaily: false,
     showCompleted: true,
     showIgnored: false,
diff --git a/test/views.test.tsx b/test/views.test.tsx
index 0214aba..0bea4aa 100644
--- a/test/views.test.tsx
+++ b/test/views.test.tsx
@@ -3,6 +3,7 @@ import { renderToStaticMarkup } from "react-dom/server";
 import { NextUp } from "../src/client/components/NextUp.tsx";
 import { boardWindow } from "../src/client/components/Timeline.tsx";
 import { Welcome } from "../src/client/components/Welcome.tsx";
+import { timelineLanes } from "../src/client/state/lanes.ts";
 import { GameMetaProvider } from "../src/client/state/gameMeta.tsx";
 import { metaFor } from "../src/shared/games.ts";
 import { clockFor } from "../src/shared/time.ts";
@@ -151,3 +152,52 @@ describe("Timeline window", () => {
     expect(max).toBeGreaterThan(NOW);
   });
 });
+
+describe("timelineLanes", () => {
+  // Deliberately not in deadline order, and with a game interleaved, so the
+  // two modes cannot both pass by accident.
+  const rows = [
+    row("Closing Ceremony", "genshin", 100),
+    row("Second Wind", "hsr", 6),
+    row("Third Rail", "genshin", 30),
+    row("Open Ended", "zzz", null),
+  ];
+
+  test("by game: a lane each, and the order inside one is left alone", () => {
+    // The rows arrive sorted by whatever the reader chose in the list.
+    // Grouping them is not a licence to re-sort within a game.
+    const lanes = timelineLanes(rows, "game");
+    expect(lanes.map((l) => l.game)).toEqual(["genshin", "hsr", "zzz"]);
+    expect(lanes[0]?.rows.map((r) => r.event.title)).toEqual([
+      "Closing Ceremony",
+      "Third Rail",
+    ]);
+  });
+
+  test("ending soonest: every game in one stack, deadline order", () => {
+    const lanes = timelineLanes(rows, "ending");
+    expect(lanes).toHaveLength(1);
+    // No heading to name the game, so the renderer has to say it per bar.
+    expect(lanes[0]?.game).toBeNull();
+    expect(lanes[0]?.rows.map((r) => r.event.title)).toEqual([
+      "Second Wind",
+      "Third Rail",
+      "Closing Ceremony",
+      // An unannounced end is still on the board, behind every dated one — it
+      // is real, but it is not a deadline.
+      "Open Ended",
+    ]);
+  });
+
+  test("neither mode loses a row", () => {
+    for (const mode of ["game", "ending"] as const) {
+      const plotted = timelineLanes(rows, mode).flatMap((l) => l.rows);
+      expect(plotted).toHaveLength(rows.length);
+    }
+  });
+
+  test("an empty board is no lanes, not one empty lane", () => {
+    expect(timelineLanes([], "ending")).toEqual([]);
+    expect(timelineLanes([], "game")).toEqual([]);
+  });
+});