This thesis explores the cleantech sector in Europe, focusing on startups and the essential role of investment, innovation, and public policies in their growth. Cleantech, centered on sustainability and resource efficiency, is critical to the transition to a low-carbon economy. Startups in this field drive innovation but face significant challenges such as financing gaps, limited access to networks, and the need for favorable policies. The European cleantech ecosystem encompasses areas like renewable energy, waste management, and energy efficiency. Successful startups depend on innovation, requiring a supportive environment that provides financial resources, entrepreneurial skills, and effective policies. Europe's leadership in sustainability is supported by policies like the European Green Deal, which encourages investment in green technologies and sustainable projects, fostering the growth of cleantech startups.