Microsoft Dynamics CRM 2015 have a flexible licensing model for both on-premise and online customers, which enables customers to mix and match new licenses based on how they use the CRM 2015 functionality. CRM 2015 on-premise and online deployment offers the following types of licenses:

The following table provides details about these license-type features:

Access to Microsoft Dynamics CRM 2015 using different clients is available in all license types. Now, in CRM 2015, there is no need to buy external user licenses for external users (the users who are not employees or affiliates) unless they are not using Microsoft Dynamics CRM 2015 clients to access applications, an external user license is covered under server license for on-premise. So, if we are required to develop any portal application to expose CRM data to our customers, it can be done without an external user license.