diff --git a/og_access/og_access.info.yml b/og_access/og_access.info.yml
new file mode 100644
index 000000000..45cb18ce1
--- /dev/null
+++ b/og_access/og_access.info.yml
@@ -0,0 +1,9 @@
+name: Organic Groups access control
+description: "Enable access control for private and public groups and group content."
+package: Organic Groups
+
+core_version_requirement: ^8 || ^9
+type: module
+
+dependencies:
+  - og:og
diff --git a/og_access/og_access.install b/og_access/og_access.install
new file mode 100644
index 000000000..c39a15be7
--- /dev/null
+++ b/og_access/og_access.install
@@ -0,0 +1,16 @@
+<?php
+
+/**
+ * @file
+ * Install/update/uninstall hook implementations.
+ */
+
+declare(strict_types = 1);
+
+/**
+ * Implements hook_install().
+ */
+function og_access_install() {
+  // Mark node access permissions for rebuild.
+  node_access_needs_rebuild(TRUE);
+}
diff --git a/og_access/og_access.module b/og_access/og_access.module
new file mode 100644
index 000000000..3f2d7be92
--- /dev/null
+++ b/og_access/og_access.module
@@ -0,0 +1,217 @@
+<?php
+
+/**
+ * @file
+ * Enable access control for private and public groups and group content.
+ *
+ * @todo Handle visibility change.
+ * @todo Set group content visibility default to that of the group.
+ * @todo Move grants/access to service.
+ */
+
+declare(strict_types = 1);
+
+use Drupal\Core\Config\Entity\ConfigEntityBundleBase;
+use Drupal\Core\Entity\BundleEntityFormBase;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\node\NodeInterface;
+use Drupal\og\Og;
+use Drupal\og_access\OgAccessBundleFormAlter;
+use Drupal\og_access\OgAccess;
+
+/**
+ * Implements hook_node_grants().
+ */
+function og_access_node_grants(AccountInterface $account, $op) {
+  if ($op !== 'view') {
+    return [];
+  }
+
+  /** @var \Drupal\og\MembershipManager $membership_manager */
+  $membership_manager = \Drupal::service('og.membership_manager');
+  if ($groups = $membership_manager->getUserGroups($account->id())) {
+    foreach ($groups as $group_type => $entity_groups) {
+      /** @var \Drupal\core\Entity\EntityInterface $group */
+      foreach ($entity_groups as $group) {
+        $realm = OgAccess::OG_ACCESS_REALM . ':' . $group_type;
+        $grants[$realm][] = $group->id();
+      }
+    }
+  }
+
+  return !empty($grants) ? $grants : [];
+}
+
+/**
+ * Implements hook_node_access_records().
+ */
+function og_access_node_access_records(NodeInterface $node) {
+  if (!$node->isPublished()) {
+    // Node is unpublished, so we don't allow any group member to see it.
+    return [];
+  }
+
+  // The group IDs, that in case access is granted, will be recorded.
+  $gids = [];
+
+  if (Og::isGroup('node', $node->getType()) &&
+      $node->hasField(OgAccess::OG_ACCESS_FIELD) &&
+      !empty($node->{OgAccess::OG_ACCESS_FIELD}) && $node->{OgAccess::OG_ACCESS_FIELD}->value) {
+    // Private group.
+    $gids['node'][] = $node->id();
+  }
+
+  if ($node->hasField(OgAccess::OG_ACCESS_CONTENT_FIELD) &&
+      !empty($node->get(OgAccess::OG_ACCESS_CONTENT_FIELD))) {
+    $content_access = $node->get(OgAccess::OG_ACCESS_CONTENT_FIELD)->value;
+  }
+  else {
+    $content_access = OgAccess::OG_ACCESS_PUBLIC;
+  }
+
+  switch ($content_access) {
+    case OgAccess::OG_ACCESS_PUBLIC:
+      // Skip non-group content nodes.
+      if (!Og::isGroupContent('node', $node->getType())) {
+        break;
+      }
+
+      $has_private = FALSE;
+      /** @var \Drupal\og\OgGroupAudienceHelper $audience_helper */
+      $audience_helper = \Drupal::service('og.group_audience_helper');
+      foreach ($audience_helper->getAllGroupAudienceFields('node', $node->getType()) as $field_name => $field) {
+        foreach ($node->get($field_name)->referencedEntities() as $group) {
+          $list_gids[$group->getEntityTypeId()][] = $group->id();
+
+          if ($has_private) {
+            // We already know we have a private group, so we can avoid
+            // re-checking it.
+            continue;
+          }
+
+          if ($group->hasField(OgAccess::OG_ACCESS_FIELD) && !empty($group->get(OgAccess::OG_ACCESS_FIELD)) &&
+              $group->get(OgAccess::OG_ACCESS_FIELD)->value) {
+            $has_private = TRUE;
+          }
+        }
+      }
+      if ($has_private) {
+        $gids = array_merge_recursive($gids, $list_gids);
+      }
+      break;
+
+    case OgAccess::OG_ACCESS_PRIVATE:
+      $list_gids = [];
+      /** @var \Drupal\og\OgGroupAudienceHelper $audience_helper */
+      $audience_helper = \Drupal::service('og.group_audience_helper');
+      foreach ($audience_helper->getAllGroupAudienceFields('node', $node->getType()) as $field_name => $field) {
+        foreach ($node->get($field_name)->referencedEntities() as $group) {
+          $list_gids[$group->getEntityTypeId()][] = $group->id();
+        }
+      }
+
+      $gids = array_merge_recursive($gids, $list_gids);
+      break;
+  }
+
+  foreach ($gids as $group_type => $values) {
+    foreach ($values as $gid) {
+      $grants[] = [
+        'realm' => OgAccess::OG_ACCESS_REALM . ':' . $group_type,
+        'gid' => $gid,
+        'grant_view' => 1,
+        'grant_update' => 0,
+        'grant_delete' => 0,
+      ];
+    }
+  }
+
+  return !empty($grants) ? $grants : [];
+}
+
+/**
+ * Implements hook_form_alter().
+ */
+function og_access_form_alter(array &$form, FormStateInterface $form_state, $form_id) {
+  if ($form_state->getFormObject() instanceof BundleEntityFormBase) {
+    (new OgAccessBundleFormAlter($form_state->getFormObject()->getEntity(), \Drupal::service('string_translation')))
+      ->formAlter($form, $form_state);
+  }
+}
+
+/**
+ * Implements hook_entity_insert().
+ */
+function og_access_entity_insert(EntityInterface $entity) {
+  og_access_entity_type_save($entity);
+}
+
+/**
+ * Implements hook_entity_update().
+ */
+function og_access_entity_update(EntityInterface $entity) {
+  og_access_entity_type_save($entity);
+}
+
+/**
+ * Adds/removes the group and group content access fields.
+ *
+ * @param \Drupal\Core\Entity\EntityInterface $entity
+ *   The entity object.
+ */
+function og_access_entity_type_save(EntityInterface $entity) {
+  if (!$entity instanceof ConfigEntityBundleBase || !isset($entity->og_is_group)) {
+    return;
+  }
+
+  $bundle = $entity->id();
+  $definition = \Drupal::entityTypeManager()->getDefinition($entity->getEntityTypeId());
+  $entity_type_id = $definition->getBundleOf();
+
+  $enable_og_access = $entity->og_enable_access;
+
+  // Add/remove on the group itself.
+  $is_group = Og::isGroup($entity_type_id, $bundle);
+  if ($entity->og_is_group || $is_group) {
+    $field = FieldConfig::loadByName($entity_type_id, $bundle, OgAccess::OG_ACCESS_FIELD);
+    if (!$field && $enable_og_access) {
+      Og::createField(OgAccess::OG_ACCESS_FIELD, $entity_type_id, $bundle);
+    }
+    elseif ($field) {
+      if (!$enable_og_access || $is_group && !$entity->og_is_group) {
+        $field->delete();
+      }
+    }
+  }
+
+  // Add remove the relevant field to the group content bundle.
+  $is_group_content = Og::isGroupContent($entity_type_id, $bundle);
+  if ($entity->og_group_content_bundle || $is_group_content) {
+    $field = FieldConfig::loadByName($entity_type_id, $bundle, OgAccess::OG_ACCESS_CONTENT_FIELD);
+
+    if (!$field && $enable_og_access) {
+      Og::createField(OgAccess::OG_ACCESS_CONTENT_FIELD, $entity_type_id, $bundle);
+    }
+    elseif ($field) {
+      if (!$enable_og_access || $is_group_content && !$entity->og_group_content_bundle) {
+        $field->delete();
+      }
+    }
+  }
+}
+
+/**
+ * Implements hook_module_implements_alter().
+ */
+function og_access_module_implements_alter(&$implementations, $hook) {
+  if ($hook === 'form_alter') {
+    // Move our form alter after the og_ui one.
+    // @todo Remove once og_ui and og are merged.
+    $group = $implementations['og_access'];
+    unset($implementations['og_access']);
+    $implementations['og_access'] = $group;
+  }
+}
diff --git a/og_access/src/OgAccess.php b/og_access/src/OgAccess.php
new file mode 100644
index 000000000..548a86796
--- /dev/null
+++ b/og_access/src/OgAccess.php
@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Drupal\og_access;
+
+/**
+ * Helper class for constants.
+ */
+class OgAccess {
+
+  /**
+   * The access realm of group member.
+   */
+  const OG_ACCESS_REALM = 'og_access';
+
+  /**
+   * Group public access field.
+   */
+  const OG_ACCESS_FIELD = 'group_access';
+
+  /**
+   * Group public access field.
+   */
+  const OG_ACCESS_CONTENT_FIELD = 'group_content_access';
+
+  /**
+   * Public group/group content access.
+   */
+  const OG_ACCESS_PUBLIC = 0;
+
+  /**
+   * Private group/group content access.
+   */
+  const OG_ACCESS_PRIVATE = 1;
+
+}
diff --git a/og_access/src/OgAccessBundleFormAlter.php b/og_access/src/OgAccessBundleFormAlter.php
new file mode 100644
index 000000000..55c6b9e57
--- /dev/null
+++ b/og_access/src/OgAccessBundleFormAlter.php
@@ -0,0 +1,105 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Drupal\og_access;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\og\Og;
+use Drupal\Core\StringTranslation\TranslationInterface;
+
+/**
+ * Helper for og_access_form_alter().
+ */
+class OgAccessBundleFormAlter {
+  use StringTranslationTrait;
+
+  /**
+   * The entity bundle.
+   *
+   * @var string
+   */
+  protected $bundle;
+
+  /**
+   * The entity type ID.
+   *
+   * @var string
+   */
+  protected $entityTypeId;
+
+  /**
+   * The form entity which has been used for populating form element defaults.
+   *
+   * @var \Drupal\Core\Entity\EntityInterface
+   */
+  protected $entity;
+
+  /**
+   * Construct a BundleFormAlter object.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity object.
+   * @param Drupal\Core\StringTranslation\TranslationInterface $string_translation
+   *   The string translation object.
+   */
+  public function __construct(EntityInterface $entity, TranslationInterface $string_translation) {
+    $this->entity = $entity;
+    $this->stringTranslation = $string_translation;
+  }
+
+  /**
+   * This is a helper for og_ui_form_alter().
+   *
+   * @param array $form
+   *   The form variable.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The form state object.
+   */
+  public function formAlter(array &$form, FormStateInterface $form_state) {
+    // Example: node.
+    $this->entityTypeId = $this->entity->getEntityType()->getBundleOf();
+
+    // Example: article.
+    $this->bundle = $this->entity->id();
+
+    $form['og']['og_enable_access'] = [
+      '#type' => 'checkbox',
+      '#title' => $this->t('Restrict access to group members'),
+      '#description' => $this->t('Enable OG access control. Provides a new field that determines the group/group content visibility. Public groups can have member-only content. Any public group content belonging to a private group will be restricted to the members of that group only.'),
+      '#default_value' => $this->bundle ? $this->hasAccessControl() : FALSE,
+      '#states' => [
+        'visible' => [
+          [':input[name="og_is_group"]' => ['checked' => TRUE]],
+          [':input[name="og_group_content_bundle"]' => ['checked' => TRUE]],
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * Checks whether the existing bundle has OG access control enabled.
+   *
+   * @return bool
+   *   True if the group bundle has the OgAccess::OG_ACCESS_FIELD field -OR-
+   *        if the group content bundle has the OG_CONTENT_ACCESS_FIELD field.
+   *   False otherwise.
+   */
+  protected function hasAccessControl() {
+    $field_definitions = \Drupal::service('entity_field.manager')
+      ->getFieldDefinitions($this->entityTypeId, $this->bundle);
+
+    if (Og::isGroup($this->entityTypeId, $this->bundle)) {
+      return isset($field_definitions[OgAccess::OG_ACCESS_FIELD]);
+    }
+
+    if (Og::isGroupContent($this->entityTypeId, $this->bundle)) {
+      return isset($field_definitions[OgAccess::OG_ACCESS_CONTENT_FIELD]);
+    }
+
+    return FALSE;
+  }
+
+}
diff --git a/og_access/src/Plugin/OgFields/OgAccessField.php b/og_access/src/Plugin/OgFields/OgAccessField.php
new file mode 100644
index 000000000..d0ba276d5
--- /dev/null
+++ b/og_access/src/Plugin/OgFields/OgAccessField.php
@@ -0,0 +1,80 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Drupal\og_access\Plugin\OgFields;
+
+use Drupal\og\OgFieldBase;
+use Drupal\og\OgFieldsInterface;
+
+/**
+ * Determine if group should use default roles and permissions.
+ *
+ * @OgFields(
+ *  id = \Drupal\og_access\OgAccess::OG_ACCESS_FIELD,
+ *  type = "group",
+ *  description = @Translation("Determine access to the group.")
+ * )
+ */
+class OgAccessField extends OgFieldBase implements OgFieldsInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFieldStorageBaseDefinition(array $values = []) {
+    $values += [
+      'cardinality' => 1,
+      'settings' => [
+        'allowed_values' => [
+          0 => $this->t('Public - accessible to all site users'),
+          1 => $this->t('Private - accessible only to group members'),
+        ],
+        'allowed_values_function' => '',
+      ],
+      'type' => 'list_integer',
+    ];
+
+    return parent::getFieldStorageBaseDefinition($values);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFieldBaseDefinition(array $values = []) {
+    $values += [
+      'default_value' => [0 => ['value' => 0]],
+      'description' => $this->t('Determine access to the group.'),
+      'display_label' => TRUE,
+      'label' => $this->t('Group visibility'),
+      'required' => TRUE,
+    ];
+
+    return parent::getFieldBaseDefinition($values);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormDisplayDefinition(array $values = []) {
+    $values += [
+      'type' => 'options_buttons',
+      'settings' => [],
+      'default_value' => 0,
+    ];
+
+    return $values;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getViewDisplayDefinition(array $values = []) {
+    $values += [
+      'type' => 'list_default',
+      'label' => 'above',
+    ];
+
+    return $values;
+  }
+
+}
diff --git a/og_access/src/Plugin/OgFields/OgContentAccessField.php b/og_access/src/Plugin/OgFields/OgContentAccessField.php
new file mode 100644
index 000000000..dc40cda58
--- /dev/null
+++ b/og_access/src/Plugin/OgFields/OgContentAccessField.php
@@ -0,0 +1,80 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Drupal\og_access\Plugin\OgFields;
+
+use Drupal\og\OgFieldBase;
+use Drupal\og\OgFieldsInterface;
+
+/**
+ * Determine the group content visibility.
+ *
+ * @OgFields(
+ *  id = \Drupal\og_access\OgAccess::OG_ACCESS_CONTENT_FIELD,
+ *  type = "node",
+ *  description = @Translation("Determine the group content visibility.")
+ * )
+ */
+class OgContentAccessField extends OgFieldBase implements OgFieldsInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFieldStorageBaseDefinition(array $values = []) {
+    $values += [
+      'cardinality' => 1,
+      'settings' => [
+        'allowed_values' => [
+          0 => $this->t('Public - accessible to all site users'),
+          1 => $this->t('Private - accessible only to group members'),
+        ],
+        'allowed_values_function' => '',
+      ],
+      'type' => 'list_integer',
+    ];
+
+    return parent::getFieldStorageBaseDefinition($values);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFieldBaseDefinition(array $values = []) {
+    $values += [
+      'default_value' => [0 => ['value' => 0]],
+      'description' => $this->t('Determine the group content visibility.'),
+      'display_label' => TRUE,
+      'label' => $this->t('Group content visibility'),
+      'required' => TRUE,
+    ];
+
+    return parent::getFieldBaseDefinition($values);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormDisplayDefinition(array $values = []) {
+    $values += [
+      'type' => 'options_buttons',
+      'settings' => [],
+      'default_value' => 0,
+    ];
+
+    return $values;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getViewDisplayDefinition(array $values = []) {
+    $values += [
+      'type' => 'list_default',
+      'label' => 'above',
+    ];
+
+    return $values;
+  }
+
+}