---
title: Tracking and cookies
slug: cms-12/docs/optimizely-tracking-cookies
docTags: 
createdAt: 2026-08-10T15:55:59.000Z
---

## Cookie usage in tracking

Cookies are issued by the client website and not Optimizely's service. IDs are stored in the respective services to map the visitor to required information for each service.

The following cookie is used with tracking for Profile Store (*EPiServer.Profiles.Client* package) and Optimizely Visitor Intelligence.

| Cookie Name | Purpose                                                                                                                                             |
| ----------- | --------------------------------------------------------------------------------------------------------------------------------------------------- |
| **\_madid** | Functionality-related. Provides a unique GUID for visitors, for Profile Store (Customer Data Platform) tracking. Persistent (1 year from creation). |