Workflows lend themselves to the granular nature of services. In other words, services fulfill a very small unit of work in favor of being reusable for many different scenarios, this in turn creates the possibility of stitching together an innumerable number of outcomes as workflows, so at a very simplistic level a workflow is nothing more than a series of services glued together to fulfill a particular business process.
In the very specific case of services, many approaches have emerged to solve this workflow problem: WSFL (Web Services Flow Language), XLANG (Web Services for Business Process Design) and BPEL (Business Process Execution Language), to name a few. Among them, the one with the most traction is without a doubt BPEL, in part due to its backing not only from major industry vendors, but also from boutique shops specializing in service-oriented architectures.
