diff --git a/src/export/odsXml.test.ts b/src/export/odsXml.test.ts
new file mode 100644
index 0000000..abd65f1
--- /dev/null
+++ b/src/export/odsXml.test.ts
@@ -0,0 +1,95 @@
+import { test, expect, describe } from "bun:test";
+import {
+  buildContentXml,
+  buildManifestXml,
+  buildStylesXml,
+  escapeXml,
+  text,
+  num,
+  empty,
+  ODS_MIMETYPE,
+} from "./odsXml.ts";
+
+test("the ODS mimetype is the spreadsheet one", () => {
+  expect(ODS_MIMETYPE).toBe("application/vnd.oasis.opendocument.spreadsheet");
+});
+
+describe("escapeXml", () => {
+  test("escapes the five XML entities", () => {
+    expect(escapeXml(`<a & b> "c" 'd'`)).toBe(
+      "&lt;a &amp; b&gt; &quot;c&quot; &apos;d&apos;",
+    );
+  });
+
+  test("leaves ordinary text alone", () => {
+    expect(escapeXml("Events and Social")).toBe("Events and Social");
+  });
+});
+
+describe("buildContentXml", () => {
+  const xml = buildContentXml([
+    {
+      name: "Summary",
+      rows: [
+        [text("Post"), text("Spent")],
+        [text("Food"), num(1234.56)],
+        [text("Empty"), empty()],
+      ],
+    },
+  ]);
+
+  test("declares the spreadsheet document namespaces", () => {
+    expect(xml).toStartWith('<?xml version="1.0" encoding="UTF-8"?>');
+    expect(xml).toContain("office:document-content");
+    expect(xml).toContain("urn:oasis:names:tc:opendocument:xmlns:office:1.0");
+  });
+
+  test("names the table", () => {
+    expect(xml).toContain('table:name="Summary"');
+  });
+
+  test("writes numbers as float cells with office:value, not text", () => {
+    expect(xml).toContain('office:value-type="float" office:value="1234.56"');
+    expect(xml).not.toContain('office:value-type="string"><text:p>1234.56');
+  });
+
+  test("writes text cells as strings", () => {
+    expect(xml).toContain('office:value-type="string"><text:p>Food</text:p>');
+  });
+
+  test("writes empty cells with no value type", () => {
+    expect(xml).toContain("<table:table-cell/>");
+  });
+
+  test("escapes sheet names and cell text", () => {
+    const nasty = buildContentXml([
+      { name: 'Food & "drink"', rows: [[text("<script>")]] },
+    ]);
+    expect(nasty).toContain('table:name="Food &amp; &quot;drink&quot;"');
+    expect(nasty).toContain("&lt;script&gt;");
+  });
+
+  test("emits one table per sheet", () => {
+    const two = buildContentXml([
+      { name: "A", rows: [[text("x")]] },
+      { name: "B", rows: [[text("y")]] },
+    ]);
+    expect(two.match(/<table:table /g)).toHaveLength(2);
+  });
+
+  test("handles a sheet with no rows", () => {
+    expect(buildContentXml([{ name: "Blank", rows: [] }])).toContain('table:name="Blank"');
+  });
+});
+
+test("buildManifestXml lists all four parts", () => {
+  const manifest = buildManifestXml();
+  for (const path of ["/", "content.xml", "styles.xml"]) {
+    expect(manifest).toContain(path);
+  }
+  expect(manifest).toContain(ODS_MIMETYPE);
+});
+
+test("buildStylesXml is a well-formed styles document", () => {
+  expect(buildStylesXml()).toContain("office:document-styles");
+});
diff --git a/src/export/odsXml.ts b/src/export/odsXml.ts
new file mode 100644
index 0000000..129a610
--- /dev/null
+++ b/src/export/odsXml.ts
@@ -0,0 +1,76 @@
+export const ODS_MIMETYPE = "application/vnd.oasis.opendocument.spreadsheet";
+
+export type Cell =
+  | { kind: "text"; value: string }
+  | { kind: "number"; value: number }
+  | { kind: "empty" };
+
+export function text(value: string): Cell {
+  return { kind: "text", value };
+}
+
+export function num(value: number): Cell {
+  return { kind: "number", value };
+}
+
+export function empty(): Cell {
+  return { kind: "empty" };
+}
+
+export interface Sheet {
+  name: string;
+  rows: Cell[][];
+}
+
+export function escapeXml(value: string): string {
+  return value
+    .replace(/&/g, "&amp;")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;")
+    .replace(/'/g, "&apos;");
+}
+
+function renderCell(cell: Cell): string {
+  switch (cell.kind) {
+    case "empty":
+      return "<table:table-cell/>";
+    case "number":
+      // office:value is what makes spreadsheets treat this as a number, so the
+      // export can be summed and pivoted rather than just read.
+      return `<table:table-cell office:value-type="float" office:value="${cell.value}"><text:p>${cell.value}</text:p></table:table-cell>`;
+    case "text":
+      return `<table:table-cell office:value-type="string"><text:p>${escapeXml(cell.value)}</text:p></table:table-cell>`;
+  }
+}
+
+function renderRow(row: Cell[]): string {
+  return `<table:table-row>${row.map(renderCell).join("")}</table:table-row>`;
+}
+
+function renderSheet(sheet: Sheet): string {
+  return `<table:table table:name="${escapeXml(sheet.name)}">${sheet.rows
+    .map(renderRow)
+    .join("")}</table:table>`;
+}
+
+const CONTENT_NS = [
+  'xmlns:office="urn:oasis:names:tc:opendocument:xmlns:office:1.0"',
+  'xmlns:table="urn:oasis:names:tc:opendocument:xmlns:table:1.0"',
+  'xmlns:text="urn:oasis:names:tc:opendocument:xmlns:text:1.0"',
+  'office:version="1.3"',
+].join(" ");
+
+export function buildContentXml(sheets: Sheet[]): string {
+  return `<?xml version="1.0" encoding="UTF-8"?><office:document-content ${CONTENT_NS}><office:body><office:spreadsheet>${sheets
+    .map(renderSheet)
+    .join("")}</office:spreadsheet></office:body></office:document-content>`;
+}
+
+export function buildStylesXml(): string {
+  return `<?xml version="1.0" encoding="UTF-8"?><office:document-styles xmlns:office="urn:oasis:names:tc:opendocument:xmlns:office:1.0" office:version="1.3"><office:styles/></office:document-styles>`;
+}
+
+export function buildManifestXml(): string {
+  return `<?xml version="1.0" encoding="UTF-8"?><manifest:manifest xmlns:manifest="urn:oasis:names:tc:opendocument:xmlns:manifest:1.0" manifest:version="1.3"><manifest:file-entry manifest:full-path="/" manifest:version="1.3" manifest:media-type="${ODS_MIMETYPE}"/><manifest:file-entry manifest:full-path="content.xml" manifest:media-type="text/xml"/><manifest:file-entry manifest:full-path="styles.xml" manifest:media-type="text/xml"/></manifest:manifest>`;
+}