diff --git a/src/main/java/com/ericbouchut/learndev/admin/AccountAdminService.java b/src/main/java/com/ericbouchut/learndev/admin/AccountAdminService.java
index 2944358..5c2f1f2 100644
--- a/src/main/java/com/ericbouchut/learndev/admin/AccountAdminService.java
+++ b/src/main/java/com/ericbouchut/learndev/admin/AccountAdminService.java
@@ -1,6 +1,7 @@
 package com.ericbouchut.learndev.admin;
 
 import com.ericbouchut.learndev.audit.AuditService;
+import com.ericbouchut.learndev.auth.LoginAttemptListener;
 import com.ericbouchut.learndev.auth.RegistrationService;
 import com.ericbouchut.learndev.auth.dto.RegisterForm;
 import com.ericbouchut.learndev.user.entity.User;
@@ -80,6 +81,15 @@ public void archive(User target, User actor, String ipAddress) {
                 "Account " + target.getUserId() + " archived");
     }
 
+    /** Unlock an account locked by failed logins and reset its counter. */
+    @Transactional
+    public void unlock(User target, User actor, String ipAddress) {
+        LoginAttemptListener.unlock(target);
+        users.save(target);
+        audit.record("ACCOUNT_UNLOCKED", actor, ipAddress, true,
+                "Account " + target.getUserId() + " unlocked");
+    }
+
     /** Reactivate an archived account: the user can log in again. */
     @Transactional
     public void reactivate(User target, User actor, String ipAddress) {
diff --git a/src/main/java/com/ericbouchut/learndev/admin/AdminController.java b/src/main/java/com/ericbouchut/learndev/admin/AdminController.java
index ed0ec0d..3e1ee87 100644
--- a/src/main/java/com/ericbouchut/learndev/admin/AdminController.java
+++ b/src/main/java/com/ericbouchut/learndev/admin/AdminController.java
@@ -132,6 +132,26 @@ public String archiveAccount(
         return "redirect:/admin/users?archived";
     }
 
+    /**
+     * Unlock an account locked by failed logins (PRG with an
+     * {@code unlocked} flag).
+     *
+     * @param userId    the account to unlock
+     * @param principal the logged-in admin
+     * @param request   provides the client IP for the audit trail
+     * @return a redirect to the account list
+     */
+    @PostMapping("/users/{userId}/unlock")
+    public String unlockAccount(
+            @PathVariable UUID userId,
+            Principal principal,
+            HttpServletRequest request
+    ) {
+        accounts.unlock(accounts.account(userId),
+                currentUser(principal), request.getRemoteAddr());
+        return "redirect:/admin/users?unlocked";
+    }
+
     /**
      * Reactivate an account (PRG with a {@code reactivated} flag).
      *
diff --git a/src/main/java/com/ericbouchut/learndev/auth/LoginAttemptListener.java b/src/main/java/com/ericbouchut/learndev/auth/LoginAttemptListener.java
new file mode 100644
index 0000000..19eaa8f
--- /dev/null
+++ b/src/main/java/com/ericbouchut/learndev/auth/LoginAttemptListener.java
@@ -0,0 +1,80 @@
+package com.ericbouchut.learndev.auth;
+
+import com.ericbouchut.learndev.audit.AuditService;
+import com.ericbouchut.learndev.user.entity.User;
+import com.ericbouchut.learndev.user.repository.UserRepository;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.event.EventListener;
+import org.springframework.security.authentication.event.AuthenticationFailureBadCredentialsEvent;
+import org.springframework.security.authentication.event.AuthenticationSuccessEvent;
+import org.springframework.stereotype.Component;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.time.OffsetDateTime;
+
+/**
+ * Account lockout: counts consecutive failed logins per account and locks
+ * the account at the configured threshold
+ * ({@code learndev.lockout.max-attempts}). A successful login resets the
+ * counter and stamps {@code last_login_at}. {@code is_locked} is already
+ * mapped to Spring Security's {@code accountLocked}, so a locked account is
+ * rejected at authentication time. Unlocking happens through the admin area
+ * or by completing a password reset (which proves control of the mailbox).
+ * Failures for unknown usernames are ignored: no row, no counter, and no
+ * behavior difference that could leak whether an account exists.
+ */
+@Component
+public class LoginAttemptListener {
+
+    private final UserRepository users;
+    private final AuditService audit;
+    private final int maxAttempts;
+
+    public LoginAttemptListener(
+            UserRepository users,
+            AuditService audit,
+            @Value("${learndev.lockout.max-attempts:5}") int maxAttempts
+    ) {
+        this.users = users;
+        this.audit = audit;
+        this.maxAttempts = maxAttempts;
+    }
+
+    /** Wrong password: count it, and lock the account at the threshold. */
+    @EventListener
+    @Transactional
+    public void onFailure(AuthenticationFailureBadCredentialsEvent event) {
+        String username = event.getAuthentication().getName();
+        users.findByUsername(username).ifPresent(user -> {
+            if (user.isLocked()) {
+                return;
+            }
+            user.setFailedLoginAttempts(user.getFailedLoginAttempts() + 1);
+            if (user.getFailedLoginAttempts() >= maxAttempts) {
+                user.setLocked(true);
+                audit.record("ACCOUNT_LOCKED", user, null, true,
+                        "Locked after " + user.getFailedLoginAttempts()
+                                + " failed login attempts");
+            }
+            users.save(user);
+        });
+    }
+
+    /** Successful login: reset the counter and stamp the login time. */
+    @EventListener
+    @Transactional
+    public void onSuccess(AuthenticationSuccessEvent event) {
+        String username = event.getAuthentication().getName();
+        users.findByUsername(username).ifPresent(user -> {
+            user.setFailedLoginAttempts(0);
+            user.setLastLoginAt(OffsetDateTime.now());
+            users.save(user);
+        });
+    }
+
+    /** Clear the lock and the counter (admin unlock, password reset). */
+    public static void unlock(User user) {
+        user.setLocked(false);
+        user.setFailedLoginAttempts(0);
+    }
+}
diff --git a/src/main/java/com/ericbouchut/learndev/auth/PasswordResetService.java b/src/main/java/com/ericbouchut/learndev/auth/PasswordResetService.java
index c0ad816..feccd2d 100644
--- a/src/main/java/com/ericbouchut/learndev/auth/PasswordResetService.java
+++ b/src/main/java/com/ericbouchut/learndev/auth/PasswordResetService.java
@@ -160,6 +160,9 @@ public boolean resetPassword(String rawToken, String newPassword, String ipAddre
 
         user.setPassword(passwordEncoder.encode(newPassword));
         user.setPasswordChangedAt(OffsetDateTime.now());
+        // Completing a reset proves control of the mailbox: clear any
+        // failed-login lock along with the counter.
+        LoginAttemptListener.unlock(user);
         token.setUsedAt(OffsetDateTime.now());
         // Strict single active link: consuming one kills the others too.
         invalidateOutstandingTokens(user);
diff --git a/src/main/resources/templates/admin/users.html b/src/main/resources/templates/admin/users.html
index b5847c5..f007fe5 100644
--- a/src/main/resources/templates/admin/users.html
+++ b/src/main/resources/templates/admin/users.html
@@ -43,8 +43,13 @@ <h1 class="page-title">Accounts</h1>
           <td th:text="${account.username}">username</td>
           <td th:text="${account.email}">email</td>
           <td th:text="${#strings.listJoin(account.roles.![roleName], ', ')}">STUDENT</td>
-          <td th:text="${account.active} ? 'Active' : 'Archived'">Active</td>
+          <td th:text="${!account.active} ? 'Archived' : (${account.locked} ? 'Locked' : 'Active')">Active</td>
           <td>
+            <form class="form--inline" th:if="${account.locked}"
+                  th:action="@{/admin/users/{id}/unlock(id=${account.userId})}" method="post">
+              <button class="button button--primary" type="submit">Unlock
+                <span class="visually-hidden" th:text="': ' + ${account.username}"></span></button>
+            </form>
             <!-- The self-archive guard lives in the service; hiding the
                  button for the logged-in admin avoids offering a dead end. -->
             <form th:if="${account.active && account.username != #authentication.name}"
diff --git a/src/test/java/com/ericbouchut/learndev/auth/AccountLockoutFlowTest.java b/src/test/java/com/ericbouchut/learndev/auth/AccountLockoutFlowTest.java
new file mode 100644
index 0000000..c5da96d
--- /dev/null
+++ b/src/test/java/com/ericbouchut/learndev/auth/AccountLockoutFlowTest.java
@@ -0,0 +1,101 @@
+package com.ericbouchut.learndev.auth;
+
+import com.ericbouchut.learndev.support.AbstractPostgresIT;
+import com.ericbouchut.learndev.user.entity.User;
+import com.ericbouchut.learndev.user.repository.UserRepository;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestBuilders.formLogin;
+import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.csrf;
+import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.user;
+import static org.springframework.security.test.web.servlet.response.SecurityMockMvcResultMatchers.authenticated;
+import static org.springframework.security.test.web.servlet.response.SecurityMockMvcResultMatchers.unauthenticated;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.redirectedUrl;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+/**
+ * End-to-end account lockout: repeated wrong passwords lock the account at
+ * the configured threshold, the right password no longer helps, an admin
+ * unlock clears the lock and the counter, and a successful login resets the
+ * counter and stamps {@code last_login_at}.
+ *
+ * <p>Named with the {@code Test} suffix (not {@code IT}) so Surefire runs it
+ * as part of {@code mvn test}; this project does not use the Failsafe plugin.
+ */
+@SpringBootTest(properties = {
+        // This feature does not use MongoDB; keep the test context Postgres-only.
+        "spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,"
+                + "org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration",
+        // A low threshold keeps the test readable; production uses 5.
+        "learndev.lockout.max-attempts=3"
+})
+@AutoConfigureMockMvc
+class AccountLockoutFlowTest extends AbstractPostgresIT {
+
+    @Autowired
+    MockMvc mvc;
+
+    @Autowired
+    UserRepository userRepository;
+
+    private User registeredUser(String username) throws Exception {
+        if (userRepository.findByUsername(username).isEmpty()) {
+            mvc.perform(post("/auth/register").with(csrf())
+                            .param("username", username)
+                            .param("email", username + "@example.com")
+                            .param("password", "secret12"))
+                    .andExpect(status().is3xxRedirection());
+        }
+        return userRepository.findByUsername(username).orElseThrow();
+    }
+
+    @Test
+    void repeated_failures_lock_the_account_and_the_admin_unlocks_it() throws Exception {
+        User victim = registeredUser("clumsy");
+        registeredUser("boss");
+
+        // Two wrong passwords: counted, not locked yet.
+        for (int i = 0; i < 2; i++) {
+            mvc.perform(formLogin("/auth/login").user("clumsy").password("wrong"))
+                    .andExpect(unauthenticated());
+        }
+        assertThat(userRepository.findByUsername("clumsy").orElseThrow()
+                .getFailedLoginAttempts()).isEqualTo(2);
+
+        // Third strike: locked; even the correct password is now rejected.
+        mvc.perform(formLogin("/auth/login").user("clumsy").password("wrong"))
+                .andExpect(unauthenticated());
+        assertThat(userRepository.findByUsername("clumsy").orElseThrow().isLocked()).isTrue();
+        mvc.perform(formLogin("/auth/login").user("clumsy").password("secret12"))
+                .andExpect(unauthenticated());
+
+        // The admin unlocks the account: lock and counter are cleared.
+        mvc.perform(post("/admin/users/{id}/unlock", victim.getUserId())
+                        .with(user("boss").roles("ADMIN")).with(csrf()))
+                .andExpect(redirectedUrl("/admin/users?unlocked"));
+        User unlocked = userRepository.findByUsername("clumsy").orElseThrow();
+        assertThat(unlocked.isLocked()).isFalse();
+        assertThat(unlocked.getFailedLoginAttempts()).isZero();
+
+        // The correct password works again, resets the counter, and stamps
+        // the login time.
+        mvc.perform(formLogin("/auth/login").user("clumsy").password("secret12"))
+                .andExpect(authenticated().withUsername("clumsy"));
+        assertThat(userRepository.findByUsername("clumsy").orElseThrow().getLastLoginAt())
+                .isNotNull();
+    }
+
+    @Test
+    void failures_for_unknown_usernames_change_nothing() throws Exception {
+        // No account row, no counter: the response is indistinguishable.
+        mvc.perform(formLogin("/auth/login").user("ghost").password("whatever"))
+                .andExpect(unauthenticated());
+        assertThat(userRepository.findByUsername("ghost")).isEmpty();
+    }
+}