Microsoft Outlook is a personal information manager software system from Microsoft, available as a part of the Microsoft 365 software suites. Primarily popular as an email client for businesses, Outlook also includes functions such as calendaring, task managing, contact managing, note-taking, journal logging, web browsing, and RSS news aggregation.

Individuals can use Outlook as a stand-alone application; organizations can deploy it as multi-user software (through Microsoft Exchange Server or SharePoint) for shared functions such as mailboxes, calendars, folders, data aggregation (i.e., SharePoint lists), and as appointment scheduling apps.

Other than the paid software on Windows and Mac desktops that this article talks about, the Outlook name also covers several other current software:

• Outlook on the web, formerly Outlook Web App, a web version of Microsoft Outlook, included in Microsoft 365, Exchange Server, and Exchange Online (domain outlook.office365.com)
• Outlook for Windows, a free Outlook application that is preinstalled with Windows 10 and later
• Outlook Mobile, a mobile app version of Outlook
• Outlook.com, formerly Hotmail, a free personal email service offered by Microsoft alongside a webmail client (domain outlook.live.com)