From Safari 11 and forward, Apple has implemented what they call Intelligent Tracking Prevention (ITP). This was introduced in June 2017 and released in September 2017. It will affect marketers and analysts, as this affects how various digital analytics solutions and 3^rd party marketing pixels can keep track on visitors.
In short, ITP simply blocks cookies used for cross-site tracking. ITP uses machine learning technologies to identify those cookies.

It isn’t new that Apple blocks some 3^rd party cookies, but the recent changes will directly affect some cookies set by various analytics solutions and 3^rd party marketing tags. Now Safari will only allow a 3^rd party cookie that can track cross-site usage to be used for 24 hours after visiting the domain the 3^rd party cookie was set on. After those 24 hours, the cookie is moved/blocked.
This directly affects systems like Google AdWords, Adobe Analytics and many more, as they are all cookie based. Often a combination of 1^st and 3^rd party cookies…

 

 
Tracking prevention timeline. Source: webkit.org
 

As Google runs a big advertising business, they had to respond quickly to this as it directly affects their ability to measure the ROI on AdWords campaigns. Their response was to implement a new cookie into Google Analytics, designed to keep ad tracking from Safari intact for Google AdWords campaigns.
This new cookie store information about AdWords campaigns clicked in a 1^st party cookie and allows Google Analytics to attribute a conversion happening more than 24 hours after the AdWords campaign was clicked, to that specific campaign.
This also means, that if you are running AdWords campaigns you need Google Analytics implemented on your website, and have the accounts linked, in order to measure accurate ROI for AdWords.

Solutions in Adobe Experience Cloud, such as Analytics, Target and Audience Manager, are also affected. As Adobe offers multiple ways of setting the Visitor ID cookie, it is worth to look into how you are doing it to understand the impact by ITP.

Adobe Marketing Cloud ID service uses a combination of 1^st and 3^rd party cookies. The 3^rd party cookie (set from demdex.net) are already blocked by Safari. No additional impact is made here by ITP.

1^st party cookies using own tracking-domain. Many Adobe customers uses a subdomain to their own site, such as metrics.example.com, for tracking. If an organization has 2 or more domains, using the same tracking server (metrics.example.com despite the user visits example.co.uk), ITP affects this. The cookie will only be available for 24 hours. Before ITP, this was the most accurate solution for sharing visitor ID’s across sites. Therefore, this solution is massively impacted.

Adobe also offers a 3^rd party cookie tracking method, and that isn’t directly affected by ITP as Safari already blocks 3^rd party cookies.

All this of cause only affects companies with more than 1 website, who has the need of understanding cross-site behavior. If your visitors don’t go across your different sites (if you have one site per market for example) this doesn’t change anything for you.

Key takeaways

• If you are running AdWords campaigns, ensure you have Google Analytics implemented on your site, and have the accounts linked, for accurate ROI measurement
• Cross-domain visitor identification are affected both for Google Analytics and Adobe Analytics
• Ensure you are using Marketing Cloud ID service or your own custom tracking server (stats.example.com etc.) if you are running Adobe Analytics
• Always respect privacy