diff --git a/app/controllers/users/profil_controller.rb b/app/controllers/users/profil_controller.rb
index f55752c11..2c9dd47cc 100644
--- a/app/controllers/users/profil_controller.rb
+++ b/app/controllers/users/profil_controller.rb
@@ -1,6 +1,9 @@
 module Users
   class ProfilController < UserController
+    before_action :ensure_update_email_is_authorized, only: :update_email
+
     def show
+      @waiting_merge_emails = waiting_merge_emails
       @waiting_transfers = current_user.dossiers.joins(:transfer).group('dossier_transfers.email').count.to_a
     end
 
@@ -11,13 +14,16 @@ module Users
     end
 
     def update_email
-      if current_user.instructeur? && !target_email_allowed?
-        flash.alert = t('.email_not_allowed', contact_email: CONTACT_EMAIL, requested_email: requested_email)
-      elsif current_user.update(update_email_params)
+      requested_user = User.find_by(email: requested_email)
+
+      if requested_user.present?
+        current_user.ask_for_merge(requested_user)
+        current_user.update(unconfirmed_email: nil)
+
         flash.notice = t('devise.registrations.update_needs_confirmation')
-      elsif current_user.errors&.details&.dig(:email)&.any? { |e| e[:error] == :taken }
-        UserMailer.account_already_taken(current_user, requested_email).deliver_later
-        # avoid leaking information about whether an account with this email exists or not
+      elsif current_user.update(update_email_params)
+        current_user.update(requested_merge_into: nil)
+
         flash.notice = t('devise.registrations.update_needs_confirmation')
       else
         flash.alert = current_user.errors.full_messages
@@ -32,8 +38,39 @@ module Users
       redirect_to profil_path
     end
 
+    def accept_merge
+      users_requesting_merge.each { |user| current_user.merge(user) }
+      users_requesting_merge.update_all(requested_merge_into_id: nil)
+
+      flash.notice = "Vous avez absorbé le compte #{waiting_merge_emails.join(', ')}"
+      redirect_to profil_path
+    end
+
+    def refuse_merge
+      users = users_requesting_merge
+      users.update_all(requested_merge_into_id: nil)
+
+      flash.notice = 'La fusion a été refusé'
+      redirect_to profil_path
+    end
+
     private
 
+    def waiting_merge_emails
+      users_requesting_merge.pluck(:email)
+    end
+
+    def users_requesting_merge
+      @requesting_merge ||= current_user.requested_merge_from
+    end
+
+    def ensure_update_email_is_authorized
+      if current_user.instructeur? && !target_email_allowed?
+        flash.alert = t('users.profil.ensure_update_email_is_authorized.email_not_allowed', contact_email: CONTACT_EMAIL, requested_email: requested_email)
+        redirect_to profil_path
+      end
+    end
+
     def update_email_params
       params.require(:user).permit(:email)
     end
diff --git a/app/mailers/user_mailer.rb b/app/mailers/user_mailer.rb
index 6fe55a4a0..e5b143566 100644
--- a/app/mailers/user_mailer.rb
+++ b/app/mailers/user_mailer.rb
@@ -12,10 +12,10 @@ class UserMailer < ApplicationMailer
     mail(to: user.email, subject: @subject, procedure: @procedure)
   end
 
-  def account_already_taken(user, requested_email)
+  def ask_for_merge(user, requested_email)
     @user = user
     @requested_email = requested_email
-    @subject = "Changement d’adresse email"
+    @subject = "Fusion de compte"
 
     mail(to: requested_email, subject: @subject)
   end
diff --git a/app/models/user.rb b/app/models/user.rb
index 24656f846..fba5d1190 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -28,6 +28,7 @@
 #  administrateur_id            :bigint
 #  expert_id                    :bigint
 #  instructeur_id               :bigint
+#  requested_merge_into_id      :bigint
 #
 class User < ApplicationRecord
   include EmailSanitizableConcern
@@ -48,10 +49,13 @@ class User < ApplicationRecord
   has_many :dossiers_invites, through: :invites, source: :dossier
   has_many :deleted_dossiers
   has_many :merge_logs, dependent: :destroy
+  has_many :requested_merge_from, class_name: 'User', dependent: :nullify, inverse_of: :requested_merge_into, foreign_key: :requested_merge_into_id
+
   has_one :france_connect_information, dependent: :destroy
   belongs_to :instructeur, optional: true, dependent: :destroy
   belongs_to :administrateur, optional: true, dependent: :destroy
   belongs_to :expert, optional: true, dependent: :destroy
+  belongs_to :requested_merge_into, class_name: 'User', optional: true
 
   accepts_nested_attributes_for :france_connect_information
 
@@ -218,6 +222,11 @@ class User < ApplicationRecord
     end
   end
 
+  def ask_for_merge(requested_user)
+    update(requested_merge_into: requested_user)
+    UserMailer.ask_for_merge(self, requested_user.email).deliver_later
+  end
+
   private
 
   def link_invites!
diff --git a/app/views/user_mailer/account_already_taken.haml b/app/views/user_mailer/account_already_taken.haml
deleted file mode 100644
index 826cdbb37..000000000
--- a/app/views/user_mailer/account_already_taken.haml
+++ /dev/null
@@ -1,20 +0,0 @@
-- content_for(:title, @subject)
-
-%p
-  Bonjour,
-
-%p
-  L’utilisateur « #{@user.email} » a demandé le changement de son adresse vers « #{@requested_email} ».
-
-%p
-  Malheureusement, votre compte « #{@requested_email} » existe déjà. Nous ne pouvons pas fusionner automatiquement vos comptes.
-
-%p
-  %strong Nous ne pouvons donc pas effectuer le changement d’adresse email.
-
-%p
-  Si vous n’êtes pas à l’origine de cette demande, vous pouvez ignorer ce message. Et si vous avez besoin d’assistance, n’hésitez pas à nous contacter à
-  = succeed '.' do
-    = mail_to CONTACT_EMAIL
-
-= render partial: "layouts/mailers/signature"
diff --git a/app/views/user_mailer/ask_for_merge.haml b/app/views/user_mailer/ask_for_merge.haml
new file mode 100644
index 000000000..d61072a89
--- /dev/null
+++ b/app/views/user_mailer/ask_for_merge.haml
@@ -0,0 +1,22 @@
+- content_for(:title, @subject)
+
+%p
+  Bonjour,
+
+%p
+  L’utilisateur <b>« #{@user.email} »</b> a demandé la fusion de son compte avec le votre <b>« #{@requested_email} »</b>.
+
+%p
+  Si vous désirez confirmer la fusion de ces comptes :
+
+%ol
+  %li connectez-vous avec le compte #{@requested_email}
+  %li allez sur votre page profil
+  %li acceptez la fusion
+
+%p
+  Si vous n’êtes pas à l’origine de cette demande, vous pouvez ignorer ce message. Et si vous avez besoin d’assistance, n’hésitez pas à nous contacter à
+  = succeed '.' do
+    = mail_to CONTACT_EMAIL
+
+= render partial: "layouts/mailers/signature"
diff --git a/app/views/users/profil/show.html.haml b/app/views/users/profil/show.html.haml
index 46f60a875..d7946c721 100644
--- a/app/views/users/profil/show.html.haml
+++ b/app/views/users/profil/show.html.haml
@@ -5,18 +5,30 @@
 #profil-page.container
   %h1 Profil
 
+  - if @waiting_merge_emails.any?
+    .card
+      .card-title Demande de fusion de comptes
+      %p
+        Acceptez-vous d’absorber le compte de
+        %span.email-address= @waiting_merge_emails.join(', ')
+
+      = link_to 'Refuser la fusion', refuse_merge_path, method: :post, class: 'button', data: { confirm: "Confirmez-vous le refus ?" }
+      = link_to 'Accepter la fusion', accept_merge_path, method: :post, class: 'button', data: { confirm: "Confirmez-vous la fusion des comptes ?" }
+
   .card
     .card-title Coordonnées
     %p
       Votre email est actuellement
       %span.email-address= current_user.email
-    - if current_user.unconfirmed_email.present?
-      .card.warning
-        .card-title
-          Changement en attente :
-          %span.email-address= current_user.unconfirmed_email
-        %p
-          Pour finaliser votre changement d’adresse, vérifiez vos emails et cliquez sur le lien de confirmation.
+
+    - waiting_email = current_user.unconfirmed_email || current_user.requested_merge_into&.email
+
+    - if waiting_email.present?
+      %p.mb-4
+        Changement en attente :
+        %span.email-address= waiting_email
+        %br
+        Pour finaliser votre changement d’adresse, vérifiez vos emails et cliquez sur le lien de confirmation.
 
     - if current_user.instructeur?
       %p.mb-4
diff --git a/config/locales/views/users/profil/fr.yml b/config/locales/views/users/profil/fr.yml
index 8062880ff..4c18b6d04 100644
--- a/config/locales/views/users/profil/fr.yml
+++ b/config/locales/views/users/profil/fr.yml
@@ -21,7 +21,7 @@ fr:
           <br>
           Si ce n'est pas votre cas, contactez le support&nbsp;:
           <a href="mailto:%{contact_email}">%{contact_email}</a>
-      update_email:
+      ensure_update_email_is_authorized:
         email_not_allowed: "L’email %{requested_email} ne peut être utilisé, contactez le support : <a href='mailto:%{contact_email}'>%{contact_email}</a>"
       transfer_all_dossiers:
         new_transfer: 
diff --git a/config/routes.rb b/config/routes.rb
index 249faa38c..45cd42836 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -280,6 +280,8 @@ Rails.application.routes.draw do
     get 'renew-api-token' => redirect('/profil')
     patch 'update_email' => 'profil#update_email'
     post 'transfer_all_dossiers' => 'profil#transfer_all_dossiers'
+    post 'accept_merge' => 'profil#accept_merge'
+    post 'refuse_merge' => 'profil#refuse_merge'
   end
 
   #
diff --git a/db/migrate/20211026082232_add_requested_merge_into_column_to_users.rb b/db/migrate/20211026082232_add_requested_merge_into_column_to_users.rb
new file mode 100644
index 000000000..aec5a9326
--- /dev/null
+++ b/db/migrate/20211026082232_add_requested_merge_into_column_to_users.rb
@@ -0,0 +1,5 @@
+class AddRequestedMergeIntoColumnToUsers < ActiveRecord::Migration[6.1]
+  def change
+    add_reference :users, :requested_merge_into, foreign_key: { to_table: :users }, null: true, index: true
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index ede968b34..c992f0ae8 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -794,11 +794,13 @@ ActiveRecord::Schema.define(version: 2021_10_26_131800) do
     t.bigint "administrateur_id"
     t.bigint "expert_id"
     t.string "locale"
+    t.bigint "requested_merge_into_id"
     t.index ["administrateur_id"], name: "index_users_on_administrateur_id"
     t.index ["confirmation_token"], name: "index_users_on_confirmation_token", unique: true
     t.index ["email"], name: "index_users_on_email", unique: true
     t.index ["expert_id"], name: "index_users_on_expert_id"
     t.index ["instructeur_id"], name: "index_users_on_instructeur_id"
+    t.index ["requested_merge_into_id"], name: "index_users_on_requested_merge_into_id"
     t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
     t.index ["unlock_token"], name: "index_users_on_unlock_token", unique: true
   end
@@ -868,5 +870,6 @@ ActiveRecord::Schema.define(version: 2021_10_26_131800) do
   add_foreign_key "users", "administrateurs"
   add_foreign_key "users", "experts"
   add_foreign_key "users", "instructeurs"
+  add_foreign_key "users", "users", column: "requested_merge_into_id"
   add_foreign_key "without_continuation_mails", "procedures"
 end
diff --git a/spec/controllers/users/profil_controller_spec.rb b/spec/controllers/users/profil_controller_spec.rb
index bb8cf8fcc..6e3bd3779 100644
--- a/spec/controllers/users/profil_controller_spec.rb
+++ b/spec/controllers/users/profil_controller_spec.rb
@@ -49,12 +49,16 @@ describe Users::ProfilController, type: :controller do
 
   describe 'PATCH #update_email' do
     context 'when everything is fine' do
+      let(:previous_request) { create(:user) }
+
       before do
+        user.update(requested_merge_into: previous_request)
         patch :update_email, params: { user: { email: 'loulou@lou.com' } }
         user.reload
       end
 
       it { expect(user.unconfirmed_email).to eq('loulou@lou.com') }
+      it { expect(user.requested_merge_into).to be_nil }
       it { expect(response).to redirect_to(profil_path) }
       it { expect(flash.notice).to eq(I18n.t('devise.registrations.update_needs_confirmation')) }
     end
@@ -63,16 +67,21 @@ describe Users::ProfilController, type: :controller do
       let(:existing_user) { create(:user) }
 
       before do
+        user.update(unconfirmed_email: 'unconfirmed@mail.com')
+
+        expect_any_instance_of(User).to receive(:ask_for_merge).with(existing_user)
+
         perform_enqueued_jobs do
           patch :update_email, params: { user: { email: existing_user.email } }
         end
         user.reload
       end
 
-      it { expect(user.unconfirmed_email).to be_nil }
-      it { expect(ActionMailer::Base.deliveries.last.to).to eq([existing_user.email]) }
-      it { expect(response).to redirect_to(profil_path) }
-      it { expect(flash.notice).to eq(I18n.t('devise.registrations.update_needs_confirmation')) }
+      it 'launches the merge process' do
+        expect(user.unconfirmed_email).to be_nil
+        expect(response).to redirect_to(profil_path)
+        expect(flash.notice).to eq(I18n.t('devise.registrations.update_needs_confirmation'))
+      end
     end
 
     context 'when the mail is incorrect' do
@@ -126,4 +135,38 @@ describe Users::ProfilController, type: :controller do
       expect(flash.notice).to eq("Le transfert de 3 dossiers à #{next_owner} est en cours")
     end
   end
+
+  context 'POST #accept_merge' do
+    let!(:requesting_user) { create(:user, requested_merge_into: user) }
+
+    subject { post :accept_merge }
+
+    it 'merges the account' do
+      expect_any_instance_of(User).to receive(:merge)
+
+      subject
+      requesting_user.reload
+
+      expect(requesting_user.requested_merge_into).to be_nil
+      expect(flash.notice).to include('Vous avez absorbé')
+      expect(response).to redirect_to(profil_path)
+    end
+  end
+
+  context 'POST #refuse_merge' do
+    let!(:requesting_user) { create(:user, requested_merge_into: user) }
+
+    subject { post :refuse_merge }
+
+    it 'merges the account' do
+      expect_any_instance_of(User).not_to receive(:merge)
+
+      subject
+      requesting_user.reload
+
+      expect(requesting_user.requested_merge_into).to be_nil
+      expect(flash.notice).to include('La fusion a été refusé')
+      expect(response).to redirect_to(profil_path)
+    end
+  end
 end
diff --git a/spec/mailers/previews/user_mailer_preview.rb b/spec/mailers/previews/user_mailer_preview.rb
index bf20eec17..436ac435f 100644
--- a/spec/mailers/previews/user_mailer_preview.rb
+++ b/spec/mailers/previews/user_mailer_preview.rb
@@ -8,8 +8,8 @@ class UserMailerPreview < ActionMailer::Preview
     UserMailer.new_account_warning(user, procedure)
   end
 
-  def account_already_taken
-    UserMailer.account_already_taken(user, 'dircab@territoires.gouv.fr')
+  def ask_for_merge
+    UserMailer.ask_for_merge(user, 'dircab@territoires.gouv.fr')
   end
 
   private
diff --git a/spec/mailers/user_mailer_spec.rb b/spec/mailers/user_mailer_spec.rb
index 651dcc4e8..88f4fa2dc 100644
--- a/spec/mailers/user_mailer_spec.rb
+++ b/spec/mailers/user_mailer_spec.rb
@@ -17,10 +17,10 @@ RSpec.describe UserMailer, type: :mailer do
     end
   end
 
-  describe '.account_already_taken' do
+  describe '.ask_for_merge' do
     let(:requested_email) { 'new@exemple.fr' }
 
-    subject { described_class.account_already_taken(user, requested_email) }
+    subject { described_class.ask_for_merge(user, requested_email) }
 
     it { expect(subject.to).to eq([requested_email]) }
     it { expect(subject.body).to include(requested_email) }
diff --git a/spec/system/users/change_email_spec.rb b/spec/system/users/change_email_spec.rb
index c2a8bfcf0..76ad23469 100644
--- a/spec/system/users/change_email_spec.rb
+++ b/spec/system/users/change_email_spec.rb
@@ -29,3 +29,36 @@ describe 'Changing an email' do
     expect(user.reload.email).to eq(new_email)
   end
 end
+
+describe 'Merging account' do
+  let(:old_user) { create(:user) }
+  let(:new_user) { create(:user) }
+
+  before do
+    login_as old_user, scope: :user
+  end
+
+  scenario 'is easy' do
+    visit '/profil'
+
+    fill_in :user_email, with: new_user.email
+
+    perform_enqueued_jobs do
+      click_button 'Changer mon adresse'
+    end
+
+    expect(page).to have_content(I18n.t('devise.registrations.update_needs_confirmation'))
+    expect(page).to have_content(old_user.email)
+    expect(page).to have_content(new_user.email)
+
+    login_as new_user, scope: :user
+    visit '/profil'
+
+    expect(page).to have_content("Acceptez-vous d’absorber le compte de #{old_user.email}")
+    click_on 'Accepter la fusion'
+
+    expect(page).not_to have_content(old_user.email)
+    expect(page).to have_content(new_user.email)
+    expect { old_user.reload }.to raise_error(ActiveRecord::RecordNotFound)
+  end
+end