This master thesis makes an exploratory analysis about the critical processes classification and its key performance indicators (KPI) for technological start-ups. The identification of critical processes and the definition of its KPI are tools used in the lean management methodology. The objectives of this work are: To validate the proposed classification of processes for technological start-ups by interviewing experts. To propose a set of KPI for the R&D process, which is considered here a principal process, by preparing an initial list of KPI and asking the experts’ points of view. In this work is contextualized the topic to treat with a literature review. Then, it is presented a proposal of processes classification for technological start-ups. Interviews to experts have been done for validating the proposed processes classification for technological start-ups. Additionally, they have been asked for the most relevant KPI. To do so, a list of KPI for different aspects has been presented to order them by importance. Most of the interviews validated the proposed classification, and thanks to them, a new critical processes classification is proposed for futures studies. Regarding the KPI, it has been denoted that there are different opinions for concluding results, although the methodology can be extrapolated if it is realized a major number of interviews.