The Dynamics CRM team has done a great job of producing documentation for CRM 2015. The ebook and video library are top notch.

But there are still some classic whitepapers that you should keep in your library. The following are my three favorite classic whitepapers that I still refer to on a regular basis:

1. Offline and online synchronization in Microsoft Dynamics CRM: This “nuts and bolts” whitepaper was written for CRM 4, but it is still unparalleled in explaining from a technical level how synchronization works in CRM. Most of its content still applies 7 years later.
2. Optimizing and Maintaining the Performance of a Microsoft Dynamics CRM 2011 Server: This whitepaper was written for Dynamics CRM 2011, but most of its content still applies to CRM 2015, including recommendations for CRM and SQL Server settings. And also get the related client whitepaper.
3. Improving Microsoft Dynamics CRM Performance and Securing Data With Microsoft SQL Server 2008: This document details supported encryption and compression features that can be used to encrypt data or improve performance, and is very useful for discussions with DBA’s.

These are my favorites that I still refer to on a regular basis. Got any more classics? Leave them in the comments.