diff --git a/base_tier_validation/README.rst b/base_tier_validation/README.rst
new file mode 100644
index 0000000..8e27d1d
--- /dev/null
+++ b/base_tier_validation/README.rst
@@ -0,0 +1,73 @@
+.. image:: https://img.shields.io/badge/license-AGPL--3-blue.png
+   :target: https://www.gnu.org/licenses/agpl
+   :alt: License: AGPL-3
+
+====================
+Base Tier Validation
+====================
+
+This module does not provide a functionality by itself but an abstract model
+to implement a validation process based on tiers on other models (e.g.
+purchase orders, sales orders...).
+
+**Note:** To be able to use this module in a new model you will need some
+development.
+
+See `purchase_tier_validation <https://github
+.com/OCA/purchase-workflow>`_ as an example of implementation.
+
+Configuration
+=============
+
+To configure this module, you need to:
+
+#. Go to *Settings > Technical > Tier Validations > Tier Definition*.
+#. Create as many tiers as you want for any model having tier validation
+   functionality.
+
+.. image:: https://odoo-community.org/website/image/ir.attachment/5784_f2813bd/datas
+   :alt: Try me on Runbot
+   :target: https://runbot.odoo-community.org/runbot/149/9.0
+
+Known issues / Roadmap
+======================
+
+* In odoo v11 it would be interesting to try to take advantage of ``mail.activity.mixin``.
+
+Bug Tracker
+===========
+
+Bugs are tracked on `GitHub Issues
+<https://github.com/OCA/server-tools/issues>`_. In case of trouble, please
+check there if your issue has already been reported. If you spotted it first,
+help us smash it by providing detailed and welcomed feedback.
+
+Credits
+=======
+
+Images
+------
+
+* Odoo Community Association: `Icon <https://odoo-community.org/logo.png>`_.
+
+Contributors
+------------
+
+* Lois Rilo <lois.rilo@eficent.com>
+
+Do not contact contributors directly about support or help with technical issues.
+
+Maintainer
+----------
+
+.. image:: https://odoo-community.org/logo.png
+   :alt: Odoo Community Association
+   :target: https://odoo-community.org
+
+This module is maintained by the OCA.
+
+OCA, or the Odoo Community Association, is a nonprofit organization whose
+mission is to support the collaborative development of Odoo features and
+promote its widespread use.
+
+To contribute to this module, please visit https://odoo-community.org.
diff --git a/base_tier_validation/__init__.py b/base_tier_validation/__init__.py
new file mode 100644
index 0000000..b44d765
--- /dev/null
+++ b/base_tier_validation/__init__.py
@@ -0,0 +1,4 @@
+# -*- coding: utf-8 -*-
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+
+from . import models
diff --git a/base_tier_validation/__openerp__.py b/base_tier_validation/__openerp__.py
new file mode 100644
index 0000000..ce34496
--- /dev/null
+++ b/base_tier_validation/__openerp__.py
@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Eficent Business and IT Consulting Services S.L.
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+{
+    "name": "Base Tier Validation",
+    "summary": "Implement a validation process based on tiers.",
+    "version": "9.0.1.0.0",
+    "category": "Tools",
+    "website": "https://github.com/OCA/server-tools",
+    "author": "Eficent, Odoo Community Association (OCA)",
+    "license": "AGPL-3",
+    "application": False,
+    "installable": True,
+    "depends": [
+        "base",
+    ],
+    "data": [
+        "security/ir.model.access.csv",
+        "views/tier_definition_view.xml",
+        "views/tier_review_view.xml",
+    ],
+}
diff --git a/base_tier_validation/models/__init__.py b/base_tier_validation/models/__init__.py
new file mode 100644
index 0000000..d7c418a
--- /dev/null
+++ b/base_tier_validation/models/__init__.py
@@ -0,0 +1,6 @@
+# -*- coding: utf-8 -*-
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+
+from . import tier_definition
+from . import tier_review
+from . import tier_validation
diff --git a/base_tier_validation/models/tier_definition.py b/base_tier_validation/models/tier_definition.py
new file mode 100644
index 0000000..ffa8144
--- /dev/null
+++ b/base_tier_validation/models/tier_definition.py
@@ -0,0 +1,54 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Eficent Business and IT Consulting Services S.L.
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+
+from openerp import api, fields, models
+
+
+class TierDefinition(models.Model):
+    _name = "tier.definition"
+    _rec_name = "model_id"
+
+    @api.model
+    def _get_tier_validation_model_names(self):
+        res = []
+        return res
+
+    model_id = fields.Many2one(
+        comodel_name="ir.model",
+        string="Referenced Model",
+    )
+    model = fields.Char(
+        related='model_id.model', index=True, store=True,
+    )
+    review_type = fields.Selection(
+        string="Validated by", default="individual",
+        selection=[("individual", "Specific user"),
+                   ("group", "Any user in a specific group.")]
+    )
+    reviewer_id = fields.Many2one(
+        comodel_name="res.users", string="Reviewer",
+    )
+    reviewer_group_id = fields.Many2one(
+        comodel_name="res.groups", string="Reviewer group",
+    )
+    python_code = fields.Text(
+        string='Tier Definition Expression',
+        help="Write Python code that defines when this tier confirmation "
+             "will be needed. The result of executing the expresion must be "
+             "a boolean.",
+        default="""# Available locals:\n#  - rec: current record""",
+    )
+    active = fields.Boolean(default=True)
+    sequence = fields.Integer(default=30)
+    company_id = fields.Many2one(
+        comodel_name="res.company", string="Company",
+        default=lambda self: self.env["res.company"]._company_default_get(
+            "tier.definition"),
+    )
+
+    @api.onchange('model_id')
+    def onchange_model_id(self):
+        return {'domain': {
+            'model_id': [
+                ('model', 'in', self._get_tier_validation_model_names())]}}
diff --git a/base_tier_validation/models/tier_review.py b/base_tier_validation/models/tier_review.py
new file mode 100644
index 0000000..e7afe7a
--- /dev/null
+++ b/base_tier_validation/models/tier_review.py
@@ -0,0 +1,41 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Eficent Business and IT Consulting Services S.L.
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+
+from openerp import api, fields, models
+
+
+class TierReview(models.Model):
+    _name = "tier.review"
+
+    status = fields.Selection(
+        selection=[("pending", "Pending"),
+                   ("rejected", "Rejected"),
+                   ("approved", "Approved")],
+        default="pending",
+    )
+    model = fields.Char(string='Related Document Model', index=True)
+    res_id = fields.Integer(string='Related Document ID', index=True)
+    definition_id = fields.Many2one(
+        comodel_name="tier.definition",
+    )
+    review_type = fields.Selection(
+        related="definition_id.review_type", readonly=True,
+    )
+    reviewer_id = fields.Many2one(
+        related="definition_id.reviewer_id", readonly=True,
+    )
+    reviewer_group_id = fields.Many2one(
+        related="definition_id.reviewer_group_id", readonly=True,
+    )
+    reviewer_ids = fields.Many2many(
+        string="Reviewers", comodel_name="res.users",
+        compute="_compute_reviewer_ids", store=True,
+    )
+    sequence = fields.Integer(string="Tier")
+
+    @api.multi
+    @api.depends('reviewer_id', 'reviewer_group_id', 'reviewer_group_id.users')
+    def _compute_reviewer_ids(self):
+        for rec in self:
+            rec.reviewer_ids = rec.reviewer_id + rec.reviewer_group_id.users
diff --git a/base_tier_validation/models/tier_validation.py b/base_tier_validation/models/tier_validation.py
new file mode 100644
index 0000000..027ceff
--- /dev/null
+++ b/base_tier_validation/models/tier_validation.py
@@ -0,0 +1,134 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Eficent Business and IT Consulting Services S.L.
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+
+from openerp import api, fields, models, _
+from openerp.exceptions import ValidationError, UserError
+from openerp.tools.safe_eval import safe_eval
+
+
+class TierValidation(models.AbstractModel):
+    _name = "tier.validation"
+
+    _state_field = 'state'
+    _state_from = ['draft']
+    _state_to = ['confirmed']
+    _cancel_state = 'cancel'
+
+    # TODO: reset validation?
+    # TODO: step by step validation?
+
+    review_ids = fields.One2many(
+        comodel_name='tier.review', inverse_name='res_id',
+        string='Validations',
+        domain=lambda self: [('model', '=', self._name)],
+        auto_join=True,
+    )
+    validated = fields.Boolean(compute="_compute_validated_rejected")
+    need_validation = fields.Boolean(compute="_compute_need_validation")
+    rejected = fields.Boolean(compute="_compute_validated_rejected")
+    reviewer_ids = fields.Many2many(
+        string="Reviewers", comodel_name="res.users",
+        compute="_compute_reviewer_ids",
+        search="_search_reviewer_ids",
+    )
+
+    @api.multi
+    @api.depends('review_ids')
+    def _compute_reviewer_ids(self):
+        for rec in self:
+            rec.reviewer_ids = rec.review_ids.filtered(
+                lambda r: r.status == 'pending').mapped('reviewer_ids')
+
+    @api.model
+    def _search_reviewer_ids(self, operator, value):
+        reviews = self.env['tier.review'].search([
+            ('model', '=', self._name), ('reviewer_ids', operator, value)])
+        return [('id', 'in', list(set(reviews.mapped('res_id'))))]
+
+    @api.multi
+    def _compute_validated_rejected(self):
+        """Override for different validation/rejection policy."""
+        for rec in self:
+            # sort by tier
+            rec.validated = not any(
+                [s != 'approved' for s in self.review_ids.mapped('status')])
+            rec.rejected = any(
+                [s == 'rejected' for s in self.review_ids.mapped('status')])
+
+    @api.multi
+    def _compute_need_validation(self):
+        for rec in self:
+            rec.need_validation = not self.review_ids and self.env[
+                'tier.definition'].search([('model', '=', self._name)]) and \
+                getattr(rec, self._state_field) in self._state_from
+
+    @api.multi
+    def evaluate_tier(self, tier):
+        try:
+            res = safe_eval(tier.python_code, globals_dict={'rec': self})
+        except Exception, error:
+            raise UserError(_(
+                "Error evaluating tier validation conditions.\n %s") % error)
+        return res
+
+    @api.multi
+    def write(self, vals):
+        for rec in self:
+            if (getattr(rec, self._state_field) in self._state_from and
+                    vals.get(self._state_field) in self._state_to):
+                if rec.need_validation:
+                    raise ValidationError(_(
+                        "This action needs to be validated for at least one "
+                        "record. \nPlease request a validation."))
+                if not rec.validated:
+                    raise ValidationError(_(
+                        "A validation process is still open for at least "
+                        "one record."))
+            if (rec.review_ids and getattr(rec, self._state_field) in
+                    self._state_from and not vals.get(self._state_field) in
+                    (self._state_to + [self._cancel_state])):
+                raise ValidationError(_("The operation is under validation."))
+        if vals.get(self._state_field) in self._state_from:
+            self.mapped('review_ids').sudo().unlink()
+        return super(TierValidation, self).write(vals)
+
+    @api.multi
+    def validate_tier(self):
+        for rec in self:
+            user_reviews = rec.review_ids.filtered(
+                lambda r: r.status in ('pending', 'rejected') and
+                (r.reviewer_id == self.env.user or
+                 r.reviewer_group_id in self.env.user.groups_id))
+            user_reviews.write({'status': 'approved'})
+
+    @api.multi
+    def reject_tier(self):
+        for rec in self:
+            user_reviews = rec.review_ids.filtered(
+                lambda r: r.status in ('pending', 'approved') and
+                (r.reviewer_id == self.env.user or
+                 r.reviewer_group_id in self.env.user.groups_id))
+            user_reviews.write({'status': 'rejected'})
+
+    @api.multi
+    def request_validation(self):
+        td_obj = self.env['tier.definition']
+        tr_obj = self.env['tier.review']
+        for rec in self:
+            if getattr(rec, self._state_field) in self._state_from:
+                if rec.need_validation:
+                    tier_definitions = td_obj.search([
+                        ('model', '=', self._name)], order="sequence desc")
+                    sequence = 0
+                    for td in tier_definitions:
+                        if self.evaluate_tier(td):
+                            sequence += 1
+                            tr_obj.create({
+                                'model': self._name,
+                                'res_id': rec.id,
+                                'definition_id': td.id,
+                                'sequence': sequence,
+                            })
+                    # TODO: notify? post some msg in chatter?
+        return True
diff --git a/base_tier_validation/security/ir.model.access.csv b/base_tier_validation/security/ir.model.access.csv
new file mode 100644
index 0000000..8491017
--- /dev/null
+++ b/base_tier_validation/security/ir.model.access.csv
@@ -0,0 +1,4 @@
+id,name,model_id:id,group_id:id,perm_read,perm_write,perm_create,perm_unlink
+access_tier_review,access.tier.review,model_tier_review,,1,1,1,1
+access_tier_definition_all,tier.definition.all,model_tier_definition,,1,0,0,0
+access_tier_definition_settings,tier.definition.settings,model_tier_definition,base.group_system,1,1,1,1
diff --git a/base_tier_validation/views/tier_definition_view.xml b/base_tier_validation/views/tier_definition_view.xml
new file mode 100644
index 0000000..5511b38
--- /dev/null
+++ b/base_tier_validation/views/tier_definition_view.xml
@@ -0,0 +1,61 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright 2017 Eficent Business and IT Consulting Services S.L.
+     License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl). -->
+<odoo>
+
+    <record id="tier_definition_view_tree" model="ir.ui.view">
+        <field name="name">tier.definition.tree</field>
+        <field name="model">tier.definition</field>
+        <field name="arch" type="xml">
+            <tree string="Tier Definition">
+                <field name="model_id"/>
+                <field name="sequence"/>
+                <field name="company_id" groups="base.group_multi_company"/>
+                <field name="active"/>
+            </tree>
+        </field>
+    </record>
+
+    <record id="tier_definition_view_form" model="ir.ui.view">
+        <field name="name">tier.definition.form</field>
+        <field name="model">tier.definition</field>
+        <field name="arch" type="xml">
+            <form string="Tier Definition">
+                <group>
+                    <group name="left">
+                        <field name="model_id" options="{'no_create': True}"/>
+                        <field name="review_type"/>
+                        <field name="reviewer_id"
+                               attrs="{'invisible': [('review_type', '!=', 'individual')]}"/>
+                        <field name="reviewer_group_id"
+                               attrs="{'invisible': [('review_type', '!=', 'group')]}"/>
+                    </group>
+                    <group name="right">
+                        <field name="company_id" groups="base.group_multi_company" options="{'no_create': True}"/>
+                        <field name="sequence"/>
+                        <field name="active"/>
+                    </group>
+                </group>
+                <group col="4" name="bottom">
+                    <field name="python_code"/>
+                </group>
+            </form>
+        </field>
+    </record>
+
+    <record id="tier_definition_action" model="ir.actions.act_window">
+        <field name="name">Tier Definition</field>
+        <field name="type">ir.actions.act_window</field>
+        <field name="res_model">tier.definition</field>
+        <field name="view_type">form</field>
+        <field name="view_mode">tree,form</field>
+    </record>
+
+    <menuitem id="menu_tier_confirmation"
+              name="Tier Validations"
+              parent="base.menu_custom"/>
+    <menuitem id="menu_tier_definition"
+              parent="menu_tier_confirmation"
+              action="tier_definition_action"/>
+
+</odoo>
diff --git a/base_tier_validation/views/tier_review_view.xml b/base_tier_validation/views/tier_review_view.xml
new file mode 100644
index 0000000..df0509f
--- /dev/null
+++ b/base_tier_validation/views/tier_review_view.xml
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright 2017 Eficent Business and IT Consulting Services S.L.
+     License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl). -->
+<odoo>
+
+    <record id="tier_review_view_tree" model="ir.ui.view">
+        <field name="name">tier.review.tree</field>
+        <field name="model">tier.review</field>
+        <field name="arch" type="xml">
+            <tree string="Tier Review"
+                  decoration-danger="status=='rejected'"
+                  decoration-success="status=='approved'">
+                <field name="sequence"/>
+                <field name="review_type"/>
+                <field name="reviewer_id"/>
+                <field name="reviewer_group_id"/>
+                <field name="status"/>
+            </tree>
+        </field>
+    </record>
+
+</odoo>