Year after year, tourism in Croatia breaks all previous records. Croatia is recording an increasing number of tourists, and that fact brings to question whether the increase in tourist arrivals is a phenomenon that can last forever. This work examines how far, if at all, the principles of sustainable tourism development have been implemented in Croatian travel agencies. The first part of the paper explains the concept of certification and it's importance in increasing efficiency and potential for profit, improving knowledge and skills, and creating reputation. At the same time, examples of good sustainability practices outside the examined sample are listed. In the next part of the paper, the key certificate for the sustainability of tourism, Travelife, is explained, which introduces structure and gives guidelines to companies which processes they implement in order to achieve the stated sustainability. The paper also cites other examples of sustainability certificates in business, as well as previous efforts of travel agencies with the implementation of sustainability. The last part of the paper summarizes previously held in-depth interviews with four travel agencies about the implementation of sustainable practices in their business and experiences with certification. The agencies were asked questions related to the assessment of the costs and benefits of certification, their effects and how to control these effects, as well as questions related to choosing partners and ultimately the main reason for the decision on certification or non-certification. The paper comes to the conclusion that the interest of travel agencies and users of travel agencies in the Republic of Croatia is almost non-existent. There are only two Travelife certified agencies in the entire country, and the representation of other certifications is also low. However, the growing trend of environmental protection gives an indication that the situation could change.