The Web Services Business Process Execution Language (WSBPEL or BPEL for short) is the standard for creating processes by orchestrating Web services. However, modeling processes, particularly large processes, is time-consuming, error-prone and therefore costly. With the growth of the number and complexity of process models in an organization, process modeling becomes a more comprehensive challenge, because it is cumbersome and not necessary for users to model every new process from scratch. Reuse has been proven to be an effective concept to improve productivity and quality in software development. With the maturing of business process management technologies, reuse in business process modeling becomes one of the important research topics in the academia and industrial communities for business process management. Reusing a piece of process logic in other processes is a desired practice based on the case studies reported in the literature. Today, subprocesses represent the only granule of reuse. However, subprocesses impose re-strictions on the syntactic and semantic completeness of the enclosed process logic. A sub-process is in general like a self-contained business process, but invoked by another business process and exhibits different degree of autonomy from the parent process. Thus, reuse of arbitrary parts of a business process, especially parts that cannot be seen as self-contained business processes, has not been addressed at the time of writing of this thesis. That kind of reuse is especially desired when creating large and complex processes. In this thesis we focus on reuse of such parts during process modeling and present a set of methods for specifying, extracting, and querying such parts of a business process and enable their reuse. We call such arbitrary parts for reuse process fragments. The contributions of this thesis are: (i) a generic conceptual definition of process fragments including a generic mathematical definition of process fragments based on a graph view; (ii) a formal definition of BPEL fragments, which shows how the generic process fragment concept can be realized within BPEL; (iii) an approach for extracting selected activities as a BPEL fragment out of a BPEL process; (iv) a generic graph-based algorithm for querying structural information of BEPL process models and fragments.