Messenger（正式名称为：MSN Messenger Service ，亦称：.NET Messenger Service和Windows Live Messenger Service）是一个由微软公司开发的即时通讯和出席系统。它与微软的.NET Passport系统一起工作使用户能与其他在线用户收发即时消息。

正式使用Messenger的客户端程序，包括Windows Live Messenger、MSN Messenger、Windows Messenger、Microsoft Messenger for Mac以及MSN Web Messenger。第三方协力商客户端程序，如Gaim、Trillian和Miranda IM也可以连上共享服务。

Messenger (formerly MSN Messenger Service, .NET Messenger Service and Windows Live Messenger Service) was an instant messaging and presence system developed by Microsoft in 1999 for use with its MSN Messenger software. It was used by instant messaging clients including Windows 8, Windows Live Messenger, Microsoft Messenger for Mac, Outlook.com and Xbox Live. Third-party clients also connected to the service. It communicated using the Microsoft Notification Protocol, a proprietary instant messaging protocol. The service allowed anyone with a Microsoft account to sign in and communicate in real time with other people who were signed in as well.