diff --git a/Cargo.lock b/Cargo.lock
index 3cac4d377..acf61c712 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1854,6 +1854,7 @@ dependencies = [
  "thiserror",
  "tokio",
  "toml",
+ "toml_edit",
  "walkdir",
 ]
 
@@ -2507,6 +2508,19 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "toml_edit"
+version = "0.25.12+spec-1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d2153edc6955a6c354fad8f5efd38b6a8769bdccf9fe50f8e1329f81b0baa5d7"
+dependencies = [
+ "indexmap",
+ "toml_datetime",
+ "toml_parser",
+ "toml_writer",
+ "winnow",
+]
+
 [[package]]
 name = "toml_parser"
 version = "1.1.2+spec-1.1.0"
@@ -3103,6 +3117,9 @@ name = "winnow"
 version = "1.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0592e1c9d151f854e6fd382574c3a0855250e1d9b2f99d9281c6e6391af352f1"
+dependencies = [
+ "memchr",
+]
 
 [[package]]
 name = "wit-bindgen"
diff --git a/Cargo.toml b/Cargo.toml
index 92582c0ea..d747c579e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -28,6 +28,7 @@ tokio = { version = "1", default-features = false, features = ["net", "rt-multi-
 tempfile = "3.19.1"
 thiserror = "2.0.18"
 toml = "1.0"
+toml_edit = "0.25"
 
 [dev-dependencies]
 ansi_term = "0.12.1"
diff --git a/src/archive.rs b/src/archive.rs
new file mode 100644
index 000000000..a78a7f63d
--- /dev/null
+++ b/src/archive.rs
@@ -0,0 +1,194 @@
+use anyhow::{Context, bail, format_err};
+use indexmap::IndexSet;
+use log::info;
+use std::path::Path;
+
+fn get_access_teams(doc: &mut toml_edit::DocumentMut) -> Option<&mut toml_edit::Table> {
+    doc.get_mut("access")?.get_mut("teams")?.as_table_mut()
+}
+
+fn archive_toml_file<F>(
+    src: &Path,
+    dest_dir: &Path,
+    dest: &Path,
+    entity: &str,
+    transform: F,
+) -> anyhow::Result<()>
+where
+    F: FnOnce(&mut toml_edit::DocumentMut),
+{
+    if !src.is_file() {
+        bail!("{entity} file not found: {}", src.display());
+    }
+    if dest.is_file() {
+        bail!("{entity} is already archived: {}", dest.display());
+    }
+
+    let mut doc = read_toml_mut(src)?;
+
+    transform(&mut doc);
+
+    std::fs::create_dir_all(dest_dir)
+        .with_context(|| format!("failed to create directory {dest_dir:?}"))?;
+    std::fs::write(dest, doc.to_string()).with_context(|| format!("failed to write {dest:?}"))?;
+    std::fs::remove_file(src).with_context(|| format!("failed to remove {src:?}"))?;
+
+    info!("archived {entity} {src:?} -> {dest:?}");
+    Ok(())
+}
+
+fn read_toml_mut(src: &Path) -> anyhow::Result<toml_edit::DocumentMut> {
+    let content =
+        std::fs::read_to_string(src).with_context(|| format!("failed to read {src:?}"))?;
+    let doc: toml_edit::DocumentMut = content
+        .parse()
+        .with_context(|| format!("failed to parse {src:?}"))?;
+    Ok(doc)
+}
+
+/// Archive a repository by moving its TOML file to `repos/archive/<org>/`
+/// and clearing every entry from the `[access.teams]` table.
+pub fn archive_repo(data_dir: &Path, name: &str) -> anyhow::Result<()> {
+    let (org, repo_name) = name
+        .split_once('/')
+        .ok_or_else(|| format_err!("repository must be in 'org/name' format, got '{name}'"))?;
+
+    let repos_dir = data_dir.join("repos");
+    let src = repos_dir.join(org).join(format!("{repo_name}.toml"));
+    let dest_dir = repos_dir.join("archive").join(org);
+    let dest = dest_dir.join(format!("{repo_name}.toml"));
+
+    archive_toml_file(&src, &dest_dir, &dest, "repo", |doc| {
+        if let Some(table) = get_access_teams(doc) {
+            table.clear();
+        }
+    })
+}
+
+/// Gather every username from a team's `leads`, `members`, and `alumni`
+/// arrays into a single deduplicated, order-preserving set.
+///
+/// Handles both bare strings (`"alice"`) and inline tables (`{ github = "alice" }`),
+/// skipping any entries that don't match either shape or that have an empty
+/// `github` field.
+fn collect_all_team_members(people_table: &toml_edit::Table) -> IndexSet<String> {
+    let mut all = IndexSet::new();
+    for key in ["leads", "members", "alumni"] {
+        let Some(arr) = people_table.get(key).and_then(|v| v.as_array()) else {
+            continue;
+        };
+        for item in arr.iter() {
+            let username = if let Some(s) = item.as_str() {
+                s.to_string()
+            } else if let Some(tbl) = item.as_inline_table() {
+                match tbl.get("github").and_then(|v| v.as_str()) {
+                    Some(s) => s.to_string(),
+                    None => continue,
+                }
+            } else {
+                continue;
+            };
+            if !username.is_empty() {
+                all.insert(username);
+            }
+        }
+    }
+    all
+}
+
+/// Build a TOML array of usernames laid out one per line with `    ` indentation
+/// and a trailing comma — matching the style used elsewhere in the team repo.
+fn build_alumni_array(usernames: &IndexSet<String>) -> toml_edit::Array {
+    let mut arr = toml_edit::Array::new();
+    for person in usernames {
+        let mut val = toml_edit::Value::from(person.as_str());
+        val.decor_mut().set_prefix("\n    ");
+        arr.push_formatted(val);
+    }
+    arr.set_trailing("\n");
+    arr.set_trailing_comma(true);
+    arr
+}
+
+/// Move everyone listed in a team's `leads`, `members`, and existing `alumni`
+/// into a single `alumni` array, leaving `leads` and `members` empty.
+///
+/// No-op if the document has no `[people]` table.
+fn move_team_members_to_alumni(doc: &mut toml_edit::DocumentMut) {
+    let Some(people_table) = doc.get_mut("people").and_then(|v| v.as_table_mut()) else {
+        return;
+    };
+
+    let all_alumni = collect_all_team_members(people_table);
+
+    people_table.insert("leads", toml_edit::Array::new().into());
+    people_table.insert("members", toml_edit::Array::new().into());
+    people_table.insert("alumni", build_alumni_array(&all_alumni).into());
+}
+
+/// Archive a team by moving its TOML file to `teams/archive/`, collapsing
+/// every `leads`/`members`/`alumni` entry into a single `alumni` array,
+/// and removing the team from every repo's `[access.teams]` table.
+pub fn archive_team(data_dir: &Path, name: &str) -> anyhow::Result<()> {
+    let teams_dir = data_dir.join("teams");
+    let src = teams_dir.join(format!("{name}.toml"));
+    let dest_dir = teams_dir.join("archive");
+    let dest = dest_dir.join(format!("{name}.toml"));
+
+    archive_toml_file(&src, &dest_dir, &dest, "team", move_team_members_to_alumni)?;
+    remove_team_from_repos(data_dir, name)?;
+    Ok(())
+}
+
+fn remove_team_from_repos(data_dir: &Path, team_name: &str) -> anyhow::Result<()> {
+    let repos_dir = data_dir.join("repos");
+    assert!(repos_dir.is_dir(), "`repos` directory does not exist");
+
+    for org_entry in
+        std::fs::read_dir(&repos_dir).with_context(|| format!("failed to read {repos_dir:?}"))?
+    {
+        let org_path = org_entry?.path();
+        assert!(
+            org_path.is_dir(),
+            "unexpected non-directory entry: `repos/{org_path:?}`"
+        );
+        if org_path.file_name() == Some(std::ffi::OsStr::new("archive")) {
+            continue;
+        }
+
+        for repo_entry in
+            std::fs::read_dir(&org_path).with_context(|| format!("failed to read {org_path:?}"))?
+        {
+            let repo_path = repo_entry?.path();
+            remove_team_from_repository(team_name, &repo_path)?;
+        }
+    }
+
+    Ok(())
+}
+
+fn remove_team_from_repository(team_name: &str, repo_path: &Path) -> anyhow::Result<()> {
+    assert!(
+        repo_path.is_file(),
+        "unexpected non-file entry: `repos/{repo_path:?}`"
+    );
+    assert!(
+        repo_path.extension() == Some(std::ffi::OsStr::new("toml")),
+        "unexpected non-TOML file: `repos/{repo_path:?}`"
+    );
+
+    let mut doc = read_toml_mut(repo_path)?;
+
+    let removed = if let Some(table) = get_access_teams(&mut doc) {
+        table.remove(team_name).is_some()
+    } else {
+        false
+    };
+
+    if removed {
+        std::fs::write(repo_path, doc.to_string())
+            .with_context(|| format!("failed to write {repo_path:?}"))?;
+        info!("removed team '{team_name}' from {repo_path:?}");
+    }
+    Ok(())
+}
diff --git a/src/main.rs b/src/main.rs
index 5dc9d51cb..14e10e494 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,6 +4,7 @@ mod data;
 #[macro_use]
 mod permissions;
 mod api;
+mod archive;
 mod ci;
 mod schema;
 mod static_api;
@@ -24,6 +25,7 @@ use api::zulip::ZulipApi;
 use data::Data;
 use schema::{Email, Team, TeamKind};
 
+use crate::archive::{archive_repo, archive_team};
 use crate::ci::{check_codeowners, generate_codeowners_file};
 use crate::schema::RepoPermission;
 use crate::sync::run_sync_team;
@@ -112,6 +114,9 @@ enum RootOpts {
     DecryptEmail,
     /// Generate a x25519 key for use with the email encryption module
     GenerateKey,
+    /// Archive a repo or team, moving it to the archive directory
+    #[clap(subcommand)]
+    Archive(ArchiveOpts),
     /// CI scripts
     #[clap(subcommand)]
     Ci(CiOpts),
@@ -139,6 +144,20 @@ enum CiOpts {
     CheckUntrackedRepos,
 }
 
+#[derive(clap::Parser, Clone, Debug)]
+enum ArchiveOpts {
+    /// Archive a repository
+    Repo {
+        /// Repository in "org/name" format (e.g. "rust-lang/homu")
+        name: String,
+    },
+    /// Archive a team
+    Team {
+        /// Team name (e.g. "project-generic-associated-types")
+        name: String,
+    },
+}
+
 #[derive(clap::Parser, Clone, Debug)]
 struct SyncOpts {
     /// Comma-separated list of available services
@@ -569,6 +588,14 @@ async fn run() -> Result<(), Error> {
             let (secret, public) = rust_team_data::email_encryption::generate_x25519_keypair();
             println!("Generated keypair: secret: {} - public: {}", secret, public);
         }
+        RootOpts::Archive(opts) => match opts {
+            ArchiveOpts::Repo { ref name } => {
+                archive_repo(&cli.data_dir, name)?;
+            }
+            ArchiveOpts::Team { ref name } => {
+                archive_team(&cli.data_dir, name)?;
+            }
+        },
         RootOpts::Ci(opts) => match opts {
             CiOpts::GenerateCodeowners => generate_codeowners_file(data)?,
             CiOpts::CheckCodeowners => check_codeowners(data)?,