University spin-offs (USOs) are an important firm class since they constitute an economically important sub-group of high-tech start-up firms: they have, consequently, engendered many academic studies. However, what the firms deliver by way of innovation in the form of new products and services has largely been missing from the academic entrepreneurship literature. By adopting a mixed research methodology of in-depth interviews and a survey, this study highlights key factors associated with the success of product and service development by USO firms in the United Kingdom -- such as understanding customer needs, networks, clear market analysis, applications of technology, and the vision, mission and value of the company. The findings resonate with various studies in innovation management on the key elements of product and service performance predictors. The article also helps to fill a gap in the academic entrepreneurship literature by providing an understanding beyond the success factors in setting up USOs. The study should therefore raise the awareness of and benefit various actors (e.g. academic entrepreneurs and technology transfer offices) with regard to the provision of the activities and skills required to develop products and services successfully.