Presently, there is a need for development of new companies and growth of existing enterprises. Likewise, there is an academic interest in Lean start-up concept. Hence, this paper investigates how potential entrepreneurs, small business owners and innovators can test and commercialise their business ideas by applying the Lean start-up technique. The main goals of this paper are to present the application of the Lean start-up method in real-life situations and show how the method can be applied by the entrepreneurs. Four small companies were observed for 3 to 5 months and five serial entrepreneurs were interviewed. Similarly, 18 best Finnish start-ups (in 2014) were surveyed. The research results showed that the technique can be used for idea and innovation testing. It was revealed that the technique could be applied to different industries though it was more applicable to technological oriented industries. Similarly, it was noted that the stages of applying the technique depend on the nature and type of product or service, the stage of start-up development and the type of start-up team. Application processes of the technique were summarised and a new process was developed. One of the authors applied the new process and it was proved that the technique could be used to commercialise business ideas.