An ASMX file is a source file format used by Microsoft's ASP.NET framework to develop and deploy web services. These files serve as the endpoint for web services that primarily communicate using the Simple Object Access Protocol (SOAP). When a web server receives a request for an ASMX file, the ASP.NET engine parses the file, compiles the associated code (typically written in C# or VB.NET), and executes the requested web method. The results are then packaged into an XML-formatted response and sent back to the client. ASMX files often contain a WebService directive at the top that links the file to a code-behind file containing the actual business logic. While ASMX was the industry standard for XML web services in the early 2000s, it has largely been replaced by more modern technologies like Windows Communication Foundation (WCF) and ASP.NET Web API, which support RESTful architectures and JSON data exchange. Despite being considered legacy, ASMX remains widely used in enterprise environments for internal services due to its simplicity and the automatic generation of Web Services Description Language (WSDL) files, which allow client applications to easily discover and consume the service's functionality.