The final thesis deals with the study and explanation of tourism in the 21st century. The thesis includes two parts, it is divided into theoretical and practical part. The theoretical part of the thesis defines the concept of tourism, states the role and function, types and forms of tourism and uses the available statistical indicators to analyze the tourism of the 21st century in the Republic of Croatia. Also, as part of the theoretical part, specific forms of tourism in the 21st century are defined, namely disaster tourism, dark tourism, opiate tourism and sex tourism. Furthermore, the practical part lists new tourism trends in the 21st century, sustainable development and green business in tourism, and the "Green Hotel" as a new concept of construction in tourism. The thesis mentions the monitoring of sustainability indicators, the role of the system of tourist boards in sustainability, and through the research methodology, the practical part of the thesis, the degree of sustainability is presented on two examples. Next, the challenges of tourism that we face in the 21st century are listed. At the end, explains the rearrangement accommodation types and standardization of the tourist offer of the 21st century.