Windows Live Messenger is Microsoft’s instant messaging client application, which works with Windows Mobile, Windows 7, Windows Vista, Windows CE, Windows XP (up to Wave 3), Xbox 360, iOS, Java ME, Symbian OS 9, x.S60, Zune HD, and Blackberry.

MSN Messenger (also known colloquially simply as MSN), later rebranded as Windows Live Messenger, was a cross-platform instant-messaging client developed by Microsoft. It connected to the now-discontinued Microsoft Messenger service and, in later versions, was compatible with Yahoo! Messenger and Facebook Messenger.

Previously called MSN Messenger, Microsoft’s Windows Live Messenger (WLM) is an advertisement-supported instant messaging service. It currently has more than 27 million active registered users worldwide. WLM offers file sharing, PC-to-PC calling, time-stamped messages, offline notifications and other features.

Microsoft's earlier instant messaging (IM) service, which provided text messaging, file sharing, and voice and video calling. Launched in 1999 as MSN Messenger, in 2005, MSN Messenger and Windows Messenger (the IM in Windows XP) were combined into one system under the Windows Live umbrella.