The Microsoft Online Services Sign-In Assistant provides end user sign-in capabilities to Microsoft Online Services, such as Office 365. The MOS SIA installs client components that allow common applications, such as Microsoft Outlook and Lync, to authenticate to Microsoft Online Services. The MOS SIA can also provide an improved sign-in experience, such that end users can access Microsoft Online Services without having to re-enter their credentials (such as a user name or password). This download is intended for IT Professionals, for distribution to managed client systems as part of an Office 365 client deployment, via System Center Configuration Manager (SCCM) or similar software distribution systems. For users who are installing Office 365 by means of the Office 365 Desktop Setup application, this download is not necessary, because the MOS SIA is installed as part of the Desktop Setup process.