The process of lean thinking implementation is difficult and resource consuming activity. Many companies, who have started the process to become lean, have failed and never achieved targets they promoted in the start. This aspect of lean philosophy has been weakly covered in lean literature and as a result companies still missing clear path to become lean. This study proposes lean implementation process for the manufacturing companies and seeks for the critical success factors of lean implementation process based on example of Estonian manufacturers. The data is gathered from semi-structured interviews, observations, field notes and company documents and then analysed and assessed. Assessment is based on lean thinking criteria with respective determinants. The results of the research prove proposed lean implementation process model and brings out that construction of company’s own production system in the form of lean house is critical in terms of success of the whole lean journey.