Use the co-authoring feature in SharePoint Server 2013 or SharePoint Online to enable multiple users to work on a document, at any time, without interfering with each other's changes. Co-authoring removes barriers to server-based document collaboration and helps organizations to reduce the overhead associated with traditional document sharing through attachments. This functionality requires no additional server setup and is the default state for documents stored in SharePoint 2013 and SharePoint Online. Co-authoring functionality is managed by using the same tools and technologies that are already used to manage SharePoint, helping to minimize the impact on administrators.
As with Office 2010, Office 2013 provides co-authoring functionality for Word 2013, PowerPoint 2013 and OneNote 2013. Office 2013 introduces co-authoring functionality for Visio 2013. If you are using SharePoint Online or have SharePoint 2013 configured to use Office Web Apps Server, users can also co-author documents in Word, PowerPoint, Excel, and OneNote Web Apps.