During the past decade the Information Technology field has experienced remarkable changes after new technologies have emerged and wireless network solutions have contributed to the development of mobile equipments and solutions. The advancements in network technologies and computing have lead to significant changes in the whole IT sector, but especially this has had a prominent influence to the software product industry. Traditionally software and applications have been sold to customer organizations and individual end-users by using license-based pricing and up-front fees. However, during the past decade people in the IT business have been able to recognize a perpetually growing interest towards service-oriented business from the software producer side, as well as from the customer side. This service orientation and development of computing resources has lead to two new phenomena: Cloud Computing and Cloud-based Software-as-a-Service (SaaS). This book will provide a comprehensive view of Cloud computing and SaaS especially from the perspective of a Custom Application Provider, and discuss the things which need to be taken into consideration when planning transition towards SaaS.