diff --git a/Cargo.lock b/Cargo.lock
index db37ed1..2d9d24e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1594,6 +1594,7 @@ dependencies = [
  "rpassword",
  "serde",
  "serde_json",
+ "tar",
  "tempfile",
  "url",
  "zeroize",
diff --git a/crates/relicario-cli/Cargo.toml b/crates/relicario-cli/Cargo.toml
index 933cd50..e56ab64 100644
--- a/crates/relicario-cli/Cargo.toml
+++ b/crates/relicario-cli/Cargo.toml
@@ -24,6 +24,7 @@ serde_json = "1"
 zeroize = "1"
 url = "2"
 data-encoding = "2"
+tar = { version = "0.4", default-features = false }
 
 [dev-dependencies]
 assert_cmd = "2"
diff --git a/crates/relicario-cli/src/main.rs b/crates/relicario-cli/src/main.rs
index 9323a5b..f0700e1 100644
--- a/crates/relicario-cli/src/main.rs
+++ b/crates/relicario-cli/src/main.rs
@@ -1289,12 +1289,160 @@ fn cmd_backup(action: BackupAction) -> Result<()> {
 }
 
 fn cmd_backup_export(
-    _out: PathBuf,
-    _include_image: bool,
-    _image: Option<PathBuf>,
-    _no_history: bool,
+    out: PathBuf,
+    include_image: bool,
+    image: Option<PathBuf>,
+    no_history: bool,
 ) -> Result<()> {
-    anyhow::bail!("cmd_backup_export not yet implemented")
+    use std::fs;
+    use relicario_core::{backup, validate_passphrase_strength};
+    use zeroize::Zeroizing;
+
+    let root = crate::helpers::vault_dir()?;
+
+    // Backup passphrase — prompt twice, gate on zxcvbn (audit H3).
+    let passphrase = if let Ok(p) = std::env::var("RELICARIO_TEST_BACKUP_PASSPHRASE") {
+        Zeroizing::new(p)
+    } else {
+        Zeroizing::new(rpassword::prompt_password("Backup passphrase: ")?)
+    };
+    let confirm = if std::env::var_os("RELICARIO_TEST_BACKUP_PASSPHRASE").is_some() {
+        passphrase.clone()
+    } else {
+        Zeroizing::new(rpassword::prompt_password("Confirm passphrase: ")?)
+    };
+    if passphrase.as_str() != confirm.as_str() {
+        anyhow::bail!("passphrases do not match");
+    }
+    if let Err(e) = validate_passphrase_strength(&passphrase) {
+        anyhow::bail!("backup {}. Choose a longer or more entropic phrase.", e);
+    }
+
+    // Read everything from disk that the envelope needs.
+    let salt = fs::read(root.join(".relicario").join("salt"))
+        .with_context(|| "failed to read .relicario/salt")?;
+    let params_json = fs::read_to_string(root.join(".relicario").join("params.json"))
+        .with_context(|| "failed to read .relicario/params.json")?;
+    let devices_json = fs::read_to_string(root.join(".relicario").join("devices.json"))
+        .with_context(|| "failed to read .relicario/devices.json")?;
+    let manifest_enc = fs::read(root.join("manifest.enc"))
+        .with_context(|| "failed to read manifest.enc")?;
+    let settings_enc = fs::read(root.join("settings.enc"))
+        .with_context(|| "failed to read settings.enc")?;
+
+    // Items.
+    let mut item_files = Vec::new();
+    let items_dir = root.join("items");
+    if items_dir.is_dir() {
+        for entry in fs::read_dir(&items_dir)? {
+            let p = entry?.path();
+            if p.extension().and_then(|s| s.to_str()) != Some("enc") { continue; }
+            let id = p.file_stem()
+                .and_then(|s| s.to_str())
+                .ok_or_else(|| anyhow::anyhow!("bad item filename: {}", p.display()))?
+                .to_string();
+            let bytes = fs::read(&p)?;
+            item_files.push((id, bytes));
+        }
+    }
+
+    // Attachments. Layout: attachments/<item_id>/<aid>.enc
+    let mut attach_files = Vec::new();
+    let attach_dir = root.join("attachments");
+    if attach_dir.is_dir() {
+        for entry in fs::read_dir(&attach_dir)? {
+            let item_dir = entry?.path();
+            if !item_dir.is_dir() { continue; }
+            let item_id = item_dir.file_name()
+                .and_then(|s| s.to_str())
+                .ok_or_else(|| anyhow::anyhow!("bad attachment dir: {}", item_dir.display()))?
+                .to_string();
+            for sub in fs::read_dir(&item_dir)? {
+                let p = sub?.path();
+                if p.extension().and_then(|s| s.to_str()) != Some("enc") { continue; }
+                let aid = p.file_stem()
+                    .and_then(|s| s.to_str())
+                    .ok_or_else(|| anyhow::anyhow!("bad attachment filename: {}", p.display()))?
+                    .to_string();
+                let bytes = fs::read(&p)?;
+                attach_files.push((item_id.clone(), aid, bytes));
+            }
+        }
+    }
+
+    // Optional reference image.
+    let image_bytes = if include_image {
+        let path = match image {
+            Some(p) => p,
+            None => crate::session::get_image_path()?,
+        };
+        Some(fs::read(&path)
+            .with_context(|| format!("failed to read reference image {}", path.display()))?)
+    } else {
+        None
+    };
+
+    // Optional .git/ tar.
+    let git_archive = if no_history { None } else { Some(tar_directory(&root.join(".git"))?) };
+
+    let items_refs: Vec<backup::BackupItem> = item_files.iter()
+        .map(|(id, bytes)| backup::BackupItem { id: id.clone(), ciphertext: bytes })
+        .collect();
+    let attach_refs: Vec<backup::BackupAttachment> = attach_files.iter()
+        .map(|(iid, aid, bytes)| backup::BackupAttachment {
+            item_id: iid.clone(),
+            attachment_id: aid.clone(),
+            ciphertext: bytes,
+        })
+        .collect();
+
+    let input = backup::BackupInput {
+        salt: &salt,
+        params_json: &params_json,
+        devices_json: &devices_json,
+        manifest_enc: &manifest_enc,
+        settings_enc: &settings_enc,
+        items: items_refs,
+        attachments: attach_refs,
+        reference_jpg: image_bytes.as_deref(),
+        git_archive: git_archive.as_deref(),
+    };
+
+    let bytes = backup::pack_backup(input, &passphrase)?;
+
+    // atomic_write via the existing pattern: write `.tmp`, rename.
+    let tmp = {
+        let mut t = out.as_os_str().to_owned();
+        t.push(".tmp");
+        PathBuf::from(t)
+    };
+    fs::write(&tmp, &bytes)
+        .with_context(|| format!("failed to write {}", tmp.display()))?;
+    fs::rename(&tmp, &out)
+        .with_context(|| format!("failed to rename {}", out.display()))?;
+
+    // Marker file for `cmd_status`. Format: ISO-8601 UTC line.
+    let now_iso = crate::helpers::iso8601(relicario_core::now_unix());
+    fs::write(root.join(".relicario").join("last_backup"), format!("{now_iso}\n"))?;
+
+    let mib = (bytes.len() as f64) / (1024.0 * 1024.0);
+    eprintln!(
+        "Wrote {} ({:.2} MiB). Delete after restore is verified.",
+        out.display(), mib
+    );
+    Ok(())
+}
+
+/// Tar a directory into an in-memory `Vec<u8>`. Used for `.git/` bundling.
+fn tar_directory(dir: &std::path::Path) -> Result<Vec<u8>> {
+    let mut buf = Vec::new();
+    {
+        let mut builder = tar::Builder::new(&mut buf);
+        builder.append_dir_all(".", dir)
+            .with_context(|| format!("failed to tar {}", dir.display()))?;
+        builder.finish()?;
+    }
+    Ok(buf)
 }
 
 fn cmd_backup_restore(_input: PathBuf, _target: PathBuf) -> Result<()> {