Microsoft BizTalk Server (or simply "BizTalk") is an Inter-Organizational Middleware System (IOMS) [3] that enables companies to automate business processes, through the use of adapters which are tailored to communicate with different software systems used in an enterprise. Created by Microsoft, it provides enterprise application integration, business process automation, business-to-business communication, message broker and business activity monitoring.

BizTalk Server was previously positioned as both an application server and an application integration server [clarify]. Microsoft changed this strategy when they released the AppFabric server which became their official application server. Research firm Gartner consider Microsoft's offering one of their 'Leaders' for Application Integration Suites. Microsoft has discontinued support for Biztalk as of 31 May 2018[4] The Azure iPaaS (integration platform as a service) equivalents to BizTalk are API Management, Logic Apps, Service Bus, and Event Grid and between November 21, 2013[6] and May 31, 2018[7] included "Azure BizTalk Services". The successor to BizTalk 2016 is on the product roadmap and slated for completion approximately 9 months following the general availability of Windows Server 2019.

In a common scenario, BizTalk enables companies to integrate and manage automated business processes by exchanging business documents such as purchase orders and invoices between disparate applications, within or across organizational boundaries.

Development for BizTalk Server is done through Microsoft Visual Studio. A developer can create transformation maps transforming one message type to another. For example, an XML file can be transformed to SAP IDocs. Messages inside BizTalk are implemented through the XML documents and defined with the XML schemas in XSD standard. Maps are implemented with the XSLT standard. Orchestrations are implemented with the WS-BPEL compatible process language xLANG. Schemas, maps, pipelines and orchestrations are created visually using graphical tools within Microsoft Visual Studio. The additional functionality can be delivered by .NET assemblies that can be called from existing modules—including, for instance, orchestrations, maps, pipelines, business rules.