OWL and SKOS are two of the Semantic Web knowledge representation languages use to represent domain knowledge. OWL has the capability of expressing richly axiomatised logicbased ontologies, due to its precise semantics that allows explicit modelling and description of a domain, and enables automated reasoning. SKOS is designed for representing knowledge organization systems, whose representation has weak semantics that are used for simple retrieval and navigation tasks. Both languages are used to represent domain knowledge at different levels and for different purposes due to different problem requirements. Knowledge captured in OWL ontology, for supporting automated reasoning could be reused for document navigation but needs to be represented in SKOS vocabulary, due to different problem requirements. In this thesis we argue each application in a particular domain has a set of problem requirements that can be fulfilled by the characteristics of the knowledge representation languages. The aim of this thesis is to improve our understanding of the OWL ontology and SKOS vocabulary landscape. Through this, understand the opportunities presented and issues encountered when transforming OWL ontologies to SKOS vocabularies. Main objective of the thesis is to understand the characteristics of OWL ontologies and SKOS vocabularies. The other objective is to explore and identify the relationships and patterns between OWL and SKOS languages and define a principled systematic procedures for transforming OWL ontologies to SKOS vocabularies. To achieve this aim, we proposed a conceptual framework that defines different possible cases for transforming knowledge artefacts between the two formalisms, OWL and SKOS. We performed with a survey of SKOS vocabularies and OWL ontologies on the Web and makes a contribution to an understanding of characteristics of both knowledge artefacts. One of the issues identified in transforming OWL ontologies to SKOS vocabularies concerns the labelling of concepts in SKOS vocabularies. Another survey on understanding the style of use of identifiers and labels in OWL ontologies was performed, contributes to understanding of labelling usage in OWL ontologies and style of lexical encodings of identifiers. We proposed a series of principled procedures for transforming OWL ontologies to SKOS vocabularies exploiting the result of the survey to deal with the labelling issues. A prototype tool, OWL2SKOS Converter, has been implemented that performs the transformation procedures and can be found here (http://owl.cs.manchester.ac.uk/owltoskos/). The work presented in this thesis should be of interest to researchers in the area of knowledge representation, who wish to exploit and reuse domain knowledge represented in formal representation like OWL ontologies to be used in applications like indexing, searching, browsing and navigation. It could also be of interest to application developers, who wish to be aware of the current practice of SKOS vocabularies.