HLA and SOA both address the problem of interoperability between dissimilar systems. While it has been perceived that they are interchangeable the paper argues that there are fundamental differences between them that need to be understood to properly evaluate them. SOA and Web Services have gained acceptance in the civilian market. Based on accepted standards like web requests and XML encoding they are easy to embrace. Web Services brings a well-specified and platform independent way for enterprise systems to exchange data that has been in demand for a long time.