The intangible nature of the tourism product where it is impossible for consumers to physically evaluate the services on offer prior to practical experience makes the availability of credible tourism recommendations very compelling. Also, the advent of new technologies like mobile computing and the semantic web has led to increased sophistication and dynamism of tourism consumer behavior. Hence, literature must find means of addressing these challenges. This book provides a new approach that leverages concepts from Software Product Line Engineering and Ontology Engineering as a way of solving these problems. It gives details of a systematic process model that enables the proactive evolution of e-tourism systems in tandem with emerging user requirements at minimal time, and development cost without performance trade-offs, while ensuring access to credible tourism recommendations. The book is relevant to the e-tourism software developers, e-tourism professionals, researchers, and students as it points the way forward on how to handle the challenges of managing dynamic user requirements, and improved quality of product recommendations in tourism.